Deadly Upgrade

The human version of Explosive Overclocking. A hero, often one who is already able to transform into a super-charged mode, discovers, is granted, or reveals that he is capable of a further transformation which gives him unstoppable power.

This transformation comes at great cost, though, as, once he uses it, it's only a matter of time before he dies, explodes, goes insane, becomes a mindless super-powered beast, or ascends to a higher plane of existence. Even if it doesn't poison him, he still may have to use his own life force to attack.

When he's forced to pull it out, his friends will have to talk him down, coaxing him into reverting to his former form. He may have to go away for a few episodes to live among the gods or somesuch.

Often, the extreme bodily stress will be demonstrated by the character's blood slowly oozing from one nostril.

Compare Heroic RROD, My Skull Runneth Over, Phlebotinum Overload and Going to Give It More Energy.

Anime

 * Goku's transformation into a giant, mindless ape in Dragon Ball. Also, the "Kai-Oh-Ken" technique from Dragonball Z risked permanent damage to Goku's body whenever he used it—especially when he overclocked it. However, thanks to My Kung Fu Is Stronger Than Yours, by the time he's fighting against Freeza, he can multiply it by twenty-fold.
 * Super Saiyan 3 is another example, a few minutes of use drained Goku of about 12 hours of his life force, and Gotenks, who burned out his 30 minute fusion in 5 minutes.
 * Dragon Ball GT reveals that by taking control of the transformation into an ape, a Saiyan can reach Super Saiyan 4, which Goku and Vegeta can maintain without exhausting themselves. However, the real problem comes when they perform a Fusion Dance into Gogeta against Omega Shenron, who has enough power to waste their galaxy if he wanted. Gogeta can use both Goku's and Vegeta's deadliest attacks as one, the first hit knocking out Omega Shenron's stolen Dragon Balls, and the second would've killed the weakened Syn Shenron... but he's too much of an idiot clown to do the job soon enough. Instead, he forgets the fusion will only last 30 minutes, and wastes precious time screwing with the dragon on cheap parlor tricks. When Gogeta does try to execute the final blow... the fusion comes undone... with less than ten minutes elapsed. And they pay for it...
 * Inuyasha's transformation into his full-demon form. His demonic blood devours a little more of his mind every time, so his demonic form becomes more and more uncontrollable. When he first transforms, he sounds like Inuyasha on a really bad day, but by the end of the series his full demon form is incapable of speech and Kagome is unable to snap him out of it.
 * And as an inversion, he can also transform into human form during the nights of the New Moon. What makes this a "Deadly Downgrade"? Simple; in human form, he loses all of his demonic powers, meaning he's easy prey for any of the demonic enemies he's made in his life... or, indeed, any true demon that realises what he is, as half-demons are almost universally despised by their full-blooded kindred.
 * Furthermore, he only transforms when facing down enemies it would take him literally seconds to kill with full power. These episodes are usually both awesome and frustrating…
 * Almost every extremely powerful technique in Naruto is some version of this.
 * The later phases of Naruto's demon transformation. The excessive amount of chakra disintegrates his body's cells, while at the same time the regeneration ability it provides heals him. In the end, it works to eat away at his lifespan. Worse, the more of the demon's power he uses, the more control of him the demon has. If he goes up to the 4-tail transformation, the demon has complete control of him, and said demon is an Omnicidal Maniac that loves killing, which results in Naruto not wanting to use its power. Not only that, but now with his
 * Tsunade possesses a technique that allows her to instantaneously regenerate, but it also speeds up her cell division and shortens her lifespan.
 * Naruto also has Rock Lee, whose power revolves solely around the Deadly Upgrade, in that he can open up certain chakra gates to gain large power boosts at the expense of damaging his body. The more gates he opens, the more injured he becomes, and if he were to open up all gates, he would become extremely powerful for a short time and then die.
 * Choji's Three Colored Pills each give as successive boost in Chakra, but burn out the user's body. The final, red pill instantly burns all the fat from his body and converts it to energy, but nearly kills him in the process. It would likely be fatal to anyone who's not as fat as he is. The pill also causes the user's cells to break down, but medicine from the Nara clan can stop the effect.
 * If he eats the last pill, he will definitely die.
 * It was revealed that.
 * causes the user's eyes to bleed when used in excess. Sasuke refuses to quit abusing the power in battle, and that leaves him almost as blind as a bat.
 * Much later there's It essentially, but at the cost of.
 * And then much, much later there's  the sister jutsu, that will , but
 * There is also the matter of how Sasuke now has sealed inside him, and the obvious dangers that entails. Fortunately,
 * Orochimaru's Curse Seal allows the person to use more chakra, and increases their attack power, but using for too long will corrupt them and the seal will completely take over. Sasuke was unusually capable of controlling this
 * In the fillers, Kagerou's Ephemeral Vengeance technique seemingly shortens her lifespan,.
 * Pain used   Later, Pain's  shortens his lifespan. Even just maintaining his Hive Mind and using any of his jutsu wrecks havoc on his real body. According to Konan, he's in danger of dying due to overexerting himself in his battle with Naruto.   Then he uses a jutsu to spoiler: [[[[Disney Death revive everyone he killed, and this ages him to death. He only gets to revitalize his body after death in Edo Tensei, using the Human Path's powers to suck in Killer B's Version 2 chakra, reversing his transformation.
 * People who possess the Death Note in the anime of the same name can give up half of their remaining life span to gain the ability to discover the true name (which, by the rules, they need to know to kill a person) of anyone whose face they can see. An even larger downside is that if they lose their Death Note, they lose the power—but also the half of their remaining life they sacrificed. If they find their Death Note again, they have to sacrifice half of their remaining life again to regain the power, meaning they'd only have 25% of their original remaining life span left.
 * In Prince of Tennis, no one's life is literally in danger, but junior high tennis is taken very seriously, so permanent physical damage may well be equal to death, or even worse.
 * One of the earlist example is the Hadoukyuu, a powerful shot that hurts the arm of whoever hits it, as well as whoever is bold, or stupid, enough to try to return it. Used initially by Ishida Tetsu, who then passes it on to Kawamura Takashi, who develops a Dash version which is even more destructive. Then we meet the big brother of Tetsu, Gin, who has 108 levels of this move, of which level ONE is equal to the Dash version. Despite this, Gin loses to a fluke which is widely seen as a cop out.
 * Tezuka Kunimitsu, widely regarded as one of the best players in the series has several Deadly Upgrades. The Zero-Shiki Drop Shot and the Invincible Tezuka Zone place considerable stress on his left arm, but he still manages to go into a 37-35 tiebreaker, which is ridiculous for tennis. Later on, these both get upgraded into a serve version, making it literally unreturnable, and a Reverse Zone, which places SIX times the burden on his arm, making it bleed a deep purplish hue by the end of the match. Obviously, none of his teammates want him to sacrifice his arm for the sake of victory, seeing that he has a promising professional career in his future. Ironically, in the matches where these are first unveiled, he loses, creating blots on an otherwise perfect official record.
 * Another ridiculous technique will ruin one's shoulders, since these players have only hit puberty, and their bodies are still maturing. Yet another one ruins the player's legs, because he's been running at hyper speeds. There's even a player who literally becomes a devil, complete with bloodshot eyes and newly-turned-white hair.
 * The most ridiculous example of this trope is the Pinnacle of Perfection, which appears to take the player who achieves this state to a higher plane of existence, but at the cost of losing all of his memories, including those of how to play tennis, rendering this upgrade, at face value, essentially useless. Currently, not surprisingly, the main character is believed to have obtained this state, seeing as how the manga is finally coming to an end. However, it turns out the Pinnacle of Perfection has no drawbacks. It is revealed that Ryoma used it during his match with Kintarou, before losing his memories. Losing his memories was because of an accident, not because of the Pinnacle of Perfection.
 * In One Piece, Tony Tony Chopper (a reindeer who can become a humanoid with the power of the Person-Person Fruit) can access four additional forms besides his animal, human, and hybrid forms with the use of pills called "Rumble Balls". However, if Chopper takes more than two Rumble Balls within six hours, he turns into a mindless hulking monster.
 * Not only is this move dangerous to those around him (due to his mindless rampaging), but it causes internal bleeding (shown by the blood coming from his mouth, despite never being harmed), making it lethal for himself as well. It's because Chopper's Monster form requires massive amounts of energy to keep going, far more than Chopper actually has. In addition, Chopper is essentially unconscious while he's in that form so he can't leave it on his own.
 * Gear Second not only drains Luffy's stamina faster than normal, but according to Rob Lucci, it shortens his lifespan by increasing his metabolism. Lucci also states that if Luffy were not a rubber man, his heart would explode if he used the technique. Of course, if he wasn't made of rubber, he probably couldn't do it in the first place.
 * It's also possible that he overcame most of the detractions after
 * In Digimon Adventure, when Greymon was pushed by Taichi into evolving, he changed into the dark SkullGreymon, a mindless monster. When he evolved "naturally", he became his true Perfect form, MetalGreymon.
 * Takato in Digimon Tamers had a similar experience: When, Takato's rage and grief is so intense that it corrupts WarGrowlmon's evolution and he becomes Megidramon, which would be fine, except Megidramon's power is so great, that it begins to destabilize the fabric of the Digital World. It's not until Takato gets a hold of himself that Megidramon devolves back into Guilmon, and together, they Matrix Evolve into Dukemon/Gallantmon.
 * In Digimon Frontier, the Beast Spirit evolutions ended up being Deadly Upgrades in a sense because the kids couldn't control the power at first and went berserk, wrecking areas and nearly killing each other. Of course, they eventually got over this problem. Only Zoe and were able to control their Beast Spirits right away.
 * Digimon Savers and its associated tamagotchi introduces Burst Mode, a Deadly Upgrade version of Season 2's Mode Change. In the tamagotchi, if the Digimon runs out of "Burst Points," it dies.
 * Ichigo in Bleach is able to throw around massively powerful kuroi getsuga tenshō energy blasts, but doing so too often risks losing his personality to his Hollow side. He can allow his Hollow side to come out in times of distress, whose violence and power is usually enough to annihilate any opponent. After training with the Vizard, he can even do so without going evil, but only for eleven seconds.
 * And in recent events, it's revealed that he's.
 * Meanwhile,
 * Cirucci Thunderwitch gains the ability to bypass her released form's drain on her spiritual by discarding her wings, enabling her to use a large energy sword from her tail at the cost of never being able to use her wings again.
 * EVA-01 and EVA-02 in Neon Genesis Evangelion were given strength and capabilities in accordance to the Sync Ratio between the pilot and machine, but the higher the values, the more likely that the pilot might suffer the injuries the mecha did, go insane, or.
 * Sailor Moon can transform into Princess Serenity and blow the Big Bad away with her silver crystal and The Power of Love... but she dies every time from all the energy output.
 * In the live-action Pretty Guardian Sailor Moon, she can upgrade to Princess Sailor Moon, in which she is possessed by Princess Serenity and has access to great power. Unfortunately, Princess Serenity is something of a sociopath in that series that doesn't care if she hurts anyone to kill the monster of the day, constantly plays a harp that is actually feeding the energy of Queen Metaria and accelerating the destruction of the planet, summon monsters to beat the crap out of her friends when they try to stop her, oh, and she's perfectly happy to destroy the world and kill everyone on it if anything happens to her lover. Needless to say, this makes Princess Serenity as much of a threat as the Dark Kingdom at the end of the series.
 * The anime Claymore almost entirely revolves around the caveat that when the series' eponymous half-demons overclock their powers too far they turn into monsters far more dangerous than those they were created to destroy; some of the more powerful of these 'awakened ones' are the primary villains of the series.
 * However, Claymores who have gone past their limit and managed to return to normal are able to do so more easily, allowing them to use more of their power, provided they don't go TOO far past their limit. However, it's theorized by said Claymores that they may still be awakening because of it, just very, very slowly.
 * The Rockman.EXE anime series did this in their final two seasons, with a twist - Rockman didn't control his transformation, a child named Trill did. Sometimes this worked out, like when Rockman was fighting the very giant Cyber Beasts he was drawing his transformation from, and sometimes it didn't, forcing the other characters to devise a complicated plan to capture him and settle him down which usually failed several times.
 * The parallel game, Mega Man Battle Network 6, played with the same mechanic. In battle, you can take the beast form for three turns, after which you drop into a weakened, untransformed state. Of course, you can do it again, which puts you totally out of control and attacking randomly, and if that doesn't win you the battle, you go into a state so tired and weakened that you have to continue the battle at a pretty significant disadvantage. Of course, it doesn't stop the writers from arranging chapters where Mega Man is forced into uncontrolled transformation and you have to lug some other character over to put him down and get him back to normal.
 * In 4 and 5, the player can gain certain "Dark Chips". They are a variation of normal chips (there's Dark Fan, Dark Vulcan and so on), but with immense power and ability to change the tide of a fight. There are, however, two drawbacks. One is that every time Mega Man uses the chip, his HP lowers by 1 permanently. Also, the more he uses Dark Chips, the faster he will be placed under "Dark Mega Man" state. He becomes a super-powerful rampaging machine that randomly uses Dark Chips, moves chaotically and doesn't stagger when being hit, but he also slowly loses HP until he reaches 1, at which point he goes back to the normal state. It's made a bit better in BN5, where you sacrifice a chip of a certain type to go into a cross form. Later on, Mega Man gets the ability to do this with Dark Chips. Chaos Unisons (as they're called) allows Mega Man to use (most) effects that he can use in a regular Cross, with the addition of being able to use the Dark Chip sacrificed as a Charged Attack. Fail the charge, though, and Dark Mega Man will show up—on the enemy's side. In addition, you only have the ability for one turn, the failure window for the charge doubles each time you use the Dark Chip, and you lose the ability to use the corresponding normal Cross for that battle.
 * In Rave Master, Sacrifar, the appropriately-named 9th form of Ten Commandments sword bestows the wielder with overwhelming power, at the cost of being gradually consumed by the sword both physically and mentally. At its first appearance, there is quite a bit of Lampshade Hanging over how crazy the man who forged the sword was to put in that form.
 * A member of the Dragon Race (like Let, Julia, or Jegan) can invoke the great power of the Dragon God, but only by sacrificing their lives to the deity.
 * The lead character of Magical Girl Lyrical Nanoha has a tendency to do things that are really bad for her, especially in the second series. This goes from using the dangerously explosive Cartridge System to using her Wave Motion Gun's full-power form, Excelion Mode. It's revealed in the third series, Magical Girl Lyrical Nanoha Strikers, that She later has her Excelion Mode replaced with a weaker Exceed Mode, which is a more traditional Super Mode. At the end of the series, however, she deploys a new Blaster Mode, which causes direct physical damage to herself and her weapon as a result of drastically boosting her power. Of course, by the time she receives this, she already has a known tendency to use techniques and upgrades that pushes her body to the breaking point, so instead of telling her not to use it, her long-time partner tells her not to overuse it.
 * In Yu-Gi-Oh!, the Spell Power Bond can double the attack strength of any Machine-type Fusion monster; however, at the end of the turn in which it is used, it decreases the user's Life Points by the original attack power of the monster. Possibly another example of Explosive Overclocking. Similarly, the Spell Limiter Removal can double the attack strength of all the user's Machine-type monsters for one turn. After which, they are destroyed.
 * In Witchblade anime use of Witchblade is shown as too taxing for a human body, and wielder of a Cloneblade sooner or later falls a victim to rapid and irreversible body deterioration ending with spectacular Superpower Meltdown. In some cases it will also corrode their mind as well. Both original and EvilKnockoffs are ClingyMacGuffins, of course.
 * In Outlaw Star, the three rare Caster Shells, numbered 4, 9, and 13, are so powerful that it also takes away part of Gene Starwind's life whenever he uses it. On a side note, 4 and 9 are considered unlucky numbers in Japanese culture, and 13 is an unlucky number in western culture.
 * Guts from Berserk has the Berserker's Armour, which draws out the full physical strength of the wearer. However, the armour also draws out the Super-Powered Evil Side of whoever wears it, and while the wearer can ignore pain, this is a double-edged sword, since the strength of whoever wears the armour will badly damage their body. Also, the armour mends broken bones by piercing through flesh with spikes. This led to the previous owner dying of blood loss after every single bone in his body was broken.
 * Upgrading one's Alter Power in S-Cry-ed includes the risk of not only dangerously messing up the user's body, but also eventually draining the user's entire life force. As the series goes on, the Upgraded Alter Power users show more and more damage to their own bodies from continual use. Kazuma and Ryuhou show scars across their bodies where their Alter Powers bond to their bodies, while Straight Cougar is actually unable to walk properly because of how messed up his legs are.
 * Alexander Anderson from Hellsing uses the Nail of Helena on himself and becomes  but using it requires him to stab himself in the heart.
 * Ryoga from Ranma ½ learns a very powerful, depression-fueled technique called the Shi Shi Hokodan, which becomes more powerful as the user gets depressed and/or miserable. This makes using it in battle rather risky, as its most powerful form basically requires the user to be so depressed that they don't care if they live or die—while the technique doesn't influence the user's mood itself (Fanon to the contrary), that does make using it against an opponent capable of outrunning or withstanding it not the brightest idea tactically. Not to mention that, when using the 'perfected' form (which fires the energy upwards as a Pillar of Light so that it drops down on the user like a Sphere of Destruction), it's possible for the attack to hit the user if they get snapped out of their moment of emotional hollowness.
 * In Mahou Sensei Negima, Negi learns a Black Magic version of this. He gets to equip spells to his body to boost strength and/or speed, depending on what he equips, at the cost of damage to his soul. The arc's Big Bad refers to it as "magical doping".
 * His master later reveals that  He is almost eerily nonplussed by that revelation, something he handwaves by pointing out that, technically, his master is , and she's still a good person.
 * also has one of these, in the form of magical runes carved on her body that release a titanic magical power when unlocked. However, doing so causes her intense pain whenever she casts something, so they're normally sealed. Akamatsu has stated that it's in some way related to the Black Magic Negi's later uses.
 * In Fairy Tail, Natsu consumes the . This brief and HUGE power boost gives Natsu the edge he needed to give the  Big Bad Gerard a beatdown. But at the start of the following arc Natsu suffers narcolepsy due to consuming non-fire related magic.
 * In Kenichi: The Mightiest Disciple, there are two kinds of aura used while fighting: Dou (letting your anger burst out) and Sei (keeping a calm and level head). It's possible to combine the two for more power, but doing so rips apart the muscles and puts heavy strain on the mind. Of the two who've used it, one ended up in a wheelchair. The other one
 * In Tekkaman Blade, D-Boy/Blade's constant transformation from human to Tekkaman and back is disintegrating his central nervous system (the other human-based Tekkamen were also going to die as a result of incompatabilities). When he gets his Super Mode upgrade, in at least the Australian version "Teknoman", the main villain comments that this upgrade causes death within a few months, and it is shown to cause D-Boy/Blade to lose memories as a result of transformation instead of having its previous deletorious effect on the central nervous system. So long as a Tekkaman was fully converted with an intact crystal then they could switch between forms with no penalty. The problem was that early on in the series D-Boy's crystal was broken and although the shards were placed on Pegas to allow transformation it was flawed and and repeated use of the flawed transformation was what caused nervous system damage to him. It also meant that so long as he used the broken crystal he'd have a time limit before going berserk. It was also true that if a human and Tekkaman plant weren't completely compatible, then they'd eventually die (which is what happened to D-Boy's sister).
 * In Mahoromatic, combat android-turned-maid Mahoro has an Ultimate Attack that is actually fueled by her life-force, so every use of it shortens her already brief lifespan.
 * Subverted in Dragon Half. Mink's power grows constantly when she pass her metamorphosis, due to be a red dragon/human hybrid, but if she achieves her maximum might and completes her metamorphosis, a prophecy states that "a black monster shall appear". A magic bracelet allows her to stop her power development at will, but against the stronger enemies she keeps facing, comes Time to Unlock More True Potential. When she finally unleash all her power to save her true love, the transformation comes? the black beast finally is showed in front of them all.
 * Using the black blood in Soul Eater is this, as the advantages given by that kind of madness (hardening the blood against injury, not caring about injuries you're receiving or giving because you're out of your mind) are negated by the consequences of doing so too much; the insanity could become permenant. Currently the heroes have gotten around this by being able to control insanity for their own uses. Whether this trick will continue to work remains to be seen.
 * The Nakatsukasa Purpose is originally seen to be this, but only because Black Star was going about using the Demon Blade mode the wrong way. Until he was beaten into re-thinking his approach, he was told explicitly that over-using the Forbidden Technique would kill him. Once Black Star chose an alternative path, using the power to protect others, he became capable of using the mode without issues.
 * Kid's Sanzu Lines could be an example of this. Fanon speculation holds that he will get the upgrade that would prove deadly to his father. If so, Shinigami is remarkably (well, not so surprising coming from him) upbeat about the prospect. As of defeating Noah with this Super Mode, Kid appears aware of the Lines connection to his father, but does not seem to know what effect the temporary upgrade has on Shinigami.
 * Speaking of blood, vampire blood in Rosario + Vampire is this to a human (Tsukune) who receives it. First, it either heals the recipient's body completely or kills him, which already makes it a last resort. Then, it temporarily gives him the powers of a vampire, but after so many uses, the change becomes permanent. Unfortunately, the blood gradually breaks down his body and mind from within, and had its progress not been stopped by a Power Limiter, he would have been turned into a rampaging ghoul. It still surfaces occasionally.
 * Cho Hakkai from Saiyuki can turn into a nearly unbeatable super-powered youkai by taking off his power limiters... but runs the very real risk of "losing himself" to the Minus Wave that's brainwashing weaker-willed youkai.
 * And the same goes for Son Goku of the same series, much like the Dragon Ball example above—fitting, since they're based on the same character from mythology.
 * In Yu Yu Hakusho, Hiei's Dragon of the Darkness Flame goes given a second use beyond basically an out of control beam attack- Hiei can let it hit him in order to absorb its power. The catch to this powered up state? It leaves him utterly drained and basically comatose for a time. Good thing he's got teammates to look after him.
 * Brave Command Dagwon has Daidouji En becoming Super Fire Dagwon only 3 times due to this. That form, while immensely powerful, requires a burst of energy from the Dagbase to even start the combination and is basically the equivalent of one person controlling two bodies - it eats up the user's stamina like nothing else. He's tough and a walking embodiment of willpower, but it still left En in a hospital bed after each use.
 * uses this in ''Fullmetal Alchemist". After receiving a massive injury during a fight, he.
 * In Ayashi no Ceres, the villains have developed some sort of serum to activate/boost the powers of potential ten'nyo, but once someone is injected with it their body begins to break down, which process seems to be accelerated by frequent use of ten'nyo powers.
 * In Puella Magi Madoka Magica,
 * Otogi Matsuri: The power granted by the Phoenix-like god named Suzaku is a mystical bow that appears as an extension of Yousuke's arm, that fires arrows of light with the power to kill evil spirits in a single shot. In exchange, Suzaku declares that it will take Yousuke's "future"... meaning that the young man only has a year left to live.
 * Otogi Matsuri: The power granted by the Phoenix-like god named Suzaku is a mystical bow that appears as an extension of Yousuke's arm, that fires arrows of light with the power to kill evil spirits in a single shot. In exchange, Suzaku declares that it will take Yousuke's "future"... meaning that the young man only has a year left to live.

Comic Books

 * This is the key premise of Strikeforce Morituri. The process that grants humans super powers against the Alien Invasion ensures that the empowered humans would also die within a year (if not sooner).
 * In X-Men related comics (her first appearance was in X-Factor) "Infectia" was a woman whose whole power was this trope. Specifically, she could mutate other people into having superpowers, but then they died within 24 hours.

Fan Works

 * Paul in With Strings Attached actually starts out with his Deadly Upgrade: he's made so strong that he can't even walk without soaring into the air and causing massive damage when he lands. He manages to shed much of the power by casting a small light spell and pumping energy into it until he explodes like a small nuke. Thereafter he is VERY wary of returning to high strength (which he finds he can do later) and practices constantly to get control of it when he does.
 * Calvin and Hobbes The Series: When Calvin gains superpowers,

Folk Lore

 * The Leanan Sidhe of Irish folklore does this. She grants inspiration to the artistic at the cost of sanity or even life.

Literature

 * Literary example: Isaac Asimov's Foundation series had a scientist character whose ability to make intuitive logical leaps was overclocked in this way by an emotion-controlling telepath, which brought him to the brink of death.
 * In A.E. Van Vogt's Isher stories, the vibratory technology that enables the Weapon Shops can also be used by humans to grow into a several hundred foot tall giant that's practically invincible... but it will also cause you to age at an exponentially increased rate. This is, of course, no impediment whatsoever to secretly immortal benevolent puppeteer of humanity Robert Hedrock.
 * The Young Wizards book series features spells of this magnitude on occasion, which involve trading part or all of the caster's life to cast.
 * There is also a "blank check" spell which will exact its price on you at a later date.
 * Performing too many complex spells without rest can fry your brain.
 * If you can get the Lone One to accept the Binding Oath, you can have temporary control over it, but there will be a backlash of negative consequences proportional to the degree of control, and you can only do this once.
 * The Sword of Truth series has "Wizard's Life Fire", an overclocked version of the already powerful Wizard's Fire that kills the user.
 * Then again, this power is typically only used when all hope is lost and you're about to be killed already. Burn the enemy off the world as they take you out.
 * There is also Con Dar, an overclocking of the Confessor's powers. It means "Blood Rage", and is only invoked on behalf of another. The main heroine survives it, but most, apparently, die after achieving their goal of revenge.
 * In the world of The Wheel of Time, all males who have magic powers gradually go insane, or begin rotting before they're dead. Doesn't help that they're generally much stronger than their female counterparts.
 * In The Curse of Chalion, the god known as The Bastard will occasionally grant a death miracle - the one who prays for someone else's death and the one who wronged him will always die. (The Bastard's death-demon can only enter or leave the world by the hole into heaven made by a death, so two deaths are required each time). A failed attempt is not fatal, but it is considered a crime of attempted murder - if the god didn't answer, the victim didn't deserve to die.
 * Everywhere in The Dresden Files, if only to prevent the eponymous character from getting Game Breaker levels of power. These include making a deal with the Leanansidhe twice, and getting shafted both times  Then there is the fallen angel whose power he could call on, but too much and he risks losing control of his body. And Soulfire, which powers his spells
 * In Mercedes Lackey's and James Mallory's The Obsidian Trilogy, there are numerous ways to do this with magic, usually by trying to do something that carries a mageprice of death (or worse). Another, more specific example comes up in the third book, where it's revealed the city Mages had developed a ritual that would grant them effectively infinite energy for their spells, but the strain of which would kill them in seven years.
 * In the latter case,
 * In David Weber's Empire from the Ashes series, the Earth defense forces give the planet itself one of these - a Core Tap (essentially a hyperspace funnel that produces ludicrous amounts of power but is highly unstable) is emplaced over Antarctica to power the planetary shield in advance of an invasion attempt (and as some idea of just how nasty one of those is, a mirosecond hiccup in power would lead to the Core Tap exploding and flattening "fifty - three percent of the landmass of the continent, tsunamis, sea level rise and the direct deaths of 6.5 million people" with indirect deaths impossible to calculate. That's half of Antarctica, a continent bigger than the US, through three kilometers of ice.) The Imperials who worked with core taps before practically faint at the idea of putting one on a planet - they aren't even safe to use in atmosphere, and it's visible in operation as a two hundred kilometer torrent of lightning that is probably harmful to the Earth even when working perfectly.
 * Lila Black from the Quantum Gravity books' original cybernetics have Battle Standard mode. This deactivates all of the safeties and limiters stopping them from ripping the user apart accidentally, goes to full power, puts the onboard AI in charge and doses the user to the point of insensibility with painkillers. It's also a bit buggy and doesn't always respond to the deactivation codes, but when you really, definitely, ABSOLUTELY HAVE to kill everything within eyesight via Macross Missile Massacre (watch the ammo expenditure), Beam Spam and Storm of Blades, and aren't particularly worried about your own survival, this should be your first port of call.
 * Lila Black from the Quantum Gravity books' original cybernetics have Battle Standard mode. This deactivates all of the safeties and limiters stopping them from ripping the user apart accidentally, goes to full power, puts the onboard AI in charge and doses the user to the point of insensibility with painkillers. It's also a bit buggy and doesn't always respond to the deactivation codes, but when you really, definitely, ABSOLUTELY HAVE to kill everything within eyesight via Macross Missile Massacre (watch the ammo expenditure), Beam Spam and Storm of Blades, and aren't particularly worried about your own survival, this should be your first port of call.

Live Action TV

 * Stargate SG-1 did this repeatedly:
 * "Upgrades" had a set of gauntlets which accelerated human metabolism to give them superspeed and superstrength, but which suppressed the users inhibitions,making them reckless. It also had a built-in time limit due to the user's immune system fighting off the virus it used to generate the effects. Of course, this has to happen at the most inconvenient time, in the middle of a mission...
 * "The Fourth Horseman": An ascended ancient reverts to human form to help SG-1, but effectively overclocks his own brain to hold on to his godlike knowledge, eventually causing severe brain damage.
 * "The Fifth Race" and "Lost City" both dealt with a device used to put information directly into one's brain; however, human brains are not advanced enough for it, and one's mind would eventually be totally overwritten by the knowledge transmitted.
 * This happens to Daniel in "The Quest", though Merlin presumably controlled the information so it wouldn't kill him. However, as Mitchell pointed out, "you don't get fancy mind powers unless there has been major redecorating going on inside your skull!"
 * The concept is lampshaded in the episode "200" where it is mentioned that to maintain the Status Quo, all that had to be done was to add a dangerous side-effect to any super-powers the characters may obtain.
 * Ascension in general in the Stargate universe. By the time you get ascended enough to actually do something, you're not allowed to. Daniel barely got away just talking to folks during his ascension and eventually gave it up so he could go back and actually do something.
 * Oma Desala taking on Anubis' ascended form in an eternal stalemate,
 * Also Stargate Atlantis—Lt. Ford is addicted to a Wraith enzyme that gives the user superior strength and durability, but causes a kind of madness. Ford's men eventually die in Wraith custody from withdrawal. McKay takes an obscenely-high amount of the enzyme, becoming a small colossus; he overpowers his guards and races back to the stargate, collapsing on the Atlantis control room floor and has to ride out the withdrawal in the infirmary.
 * Also in Stargate Atlantis, Dr. McKay gets zapped by an Ascension Machine (I defy anyone to come up with a less ridiculous description) and gets a few superpowers. But of course (in a hilarious scene) he finds out he has to ascend or die.
 * In the Doctor Who episode "The Parting of the Ways", Rose absorbs the Time Vortex, gaining godlike powers which would have killed her had the Doctor not sacrificed himself instead.
 * In the series 4 finale.
 * Angel: The deadlier sort of Hilarity Ensues when Lorne has his sleep removed for a party.
 * Albeit, unlike most other examples of this trope, this was deadly to everyone else, rather than to Lorne himself...
 * LORNE SMASH!
 * Of course, one could say Angelus himself is a form of this trope.
 * Illyria inverts it into a deadly *downgrade* sort of thing when she, a powerful Old One, revives in a human body-Fred's body can't take Illyria's power for long, and the gang has to drain some of it before she explodes and takes the whole world with her.
 * The Monster of the Week Angel faces in the Season 3 opener "Heartthrob" was James, a former vampire protege of Angelus who had removed his own heart to make himself unkillable. He sought to use his invincibility to kill Angel as revenge for his killing James' girlfriend, but the powers only lasted for six hours before he spontaneously turned to dust.
 * And Cordelia, who got the visions from Doyle, but they weren't meant for humans, and she had to let herself be made part demon before the visions either drove her insane or blew out her skull.
 * Buffy the Vampire Slayer, anyone?
 * And Buffy herself, when she became telepathic. Eventually, she got overwhelmed and went into a Heroic BSOD until the cure was given to her.
 * Star Trek: Deep Space Nine: An alien woman seduces Jake Sisko, and heightens his creativity so that she can absorb the resulting energy, causing him to write compulsively to the point of collapse and beyond. Needless to say, the heroes discover what is happening just in time to save his life.
 * Leanan Sidhe (see above) may be the inspiration.
 * In the 2000 The Invisible Man TV series, Darien Fawkes can make himself invisible by the means of "Quicksilver", a substance secreted by an artificial gland implanted in his brain—but the gland also secretes toxins that will drive him mad and kill him, if not neutralized with a shot of "counteragent."
 * This is deliberate, though. The Big Bad secreatly added a flaw into the gland in order to control anyone who buys it with a counteragent.
 * The episode with the invisible Bigfoot seems to indicate that the original gland was flawed from the beginning, as the beast is constantly enraged.
 * Most of the more recent Kamen Rider series have used this trope as a plot point.
 * In Kamen Rider Kuuga, the main character has an "ultimate form" that he can assume, at the risk of.
 * In Kamen Rider Agito, one of the riders (Gills).
 * The first version of the G3-X Armour would . The G4 Armour, while being the most powerful version, would eventually.
 * In Kamen Rider 555, the Orphenochs seem to be the embodiment of Deadly Upgrade: they are dead humans who either become Orphenochs after suffering some accidental death, or are "sired" by other Orphenochs. The process requires the human to die either way. Not only that, but they . The way to prevent this decay, however,.
 * The Kaixa Gear that most users die after a single use. The Faiz Gear works much the same way, but has a warning system that rejects users it would kill. The Delta Gear works for anyone, but carries a risk that.
 * In Kamen Rider Blade, the main character can assume his "King form" through a process that . However,.
 * In Kamen Rider Hibiki, there is a sword that can transform a Rider into an "Armed" form; however, if the Rider is not "ready" for the transformation, he loses the ability to transform.
 * In Kamen Rider Kabuto, the Big Bad . The Super Prototype Hopper Zecters seem to come with a requirement of insanity.
 * In Kamen Rider Den-O, Zeronos uses cards that to transform. Later, his Palette Swap upgrade Zero Form.
 * In Kamen Rider Kiva, the prototype IXA system puts incredible strain on its user's body, and can only be used for a short period of time before apparently overheating..
 * The power of Dark Kiva takes an even more savage toll on its user if they are an ordinary human rather than a Fangire.
 * The Fang form of Kamen Rider Double was supposed to be this, driving Philip violently insane, but it only did that once.
 * Similarly, Kamen Rider OOO can't use the three-of-a-kind combos without risking his life and sanity, supposedly, but so far there are no lasting effects (sometimes he's a little growly while using one, sometimes he faints afterward. But when you look at the above-mentioned examples of Rider powers becoming lethal or madness-inducing, when you watch OOO turn out fine in the end every time, you can't help but think "uh, weren't combos supposed to be, like, dangerous or something?")
 * The PuToTyra Form, the ultimate form of OOO, is this. Eiji is forcibly changed to this form and he has no control over its power (or himself, by extension). If all the enemies are defeated by him, don't expect him to change back yet... he'll kill anyone who's with him during the fight (as in anyone that he can see, be it friend, foe, or non-powered civilian) and Birth must fight him to keep those around him safe. Luckily, Eiji got better as he managed to control this form later on. We find, though, that there's something to the warnings about the power of OOO, though: Eiji's predecessor indeed went berserk, and those dinosaur medals . However, none of these come from simply using the suit, even with combos:  . Using Tajador in almost every episode for a while, though, never did him any harm.
 * However, before them all was Kamen Rider Stronger, the first Rider to have a Super Mode, or any form-changing at all. (If we don't count Riderman's different arm attachments, anyway.) If he uses Charge Up, he's got to burn through the extra energy in sixty seconds, or else.
 * In Mahou Sentai Magiranger, the Ozu children eventually gain the upgrade Legend Form. Unfortunately, using this form even a little will cause them to . The only way to avoid this is for.
 * In an episode of Red Dwarf, Kryten comes up with a plan to restore Holly's computer-senility-ravaged IQ to its original level at the cost of operational runtime. Due to a miscalculation, her IQ is actually doubled...but she ends up with just under four minutes to live.
 * In Farscape: The Peacekeeper Wars, John goes rather comatose after activating (and deactivating) the wormhole weapon, as the agreed-upon removal process of the implanted wormhole knowledge had the possibility of frying his brain. Doesn't mean he can't create his own version of the tech in time though.
 * In an first-season episode, a weapon known as the Gauntlet is introduced: it's capable of firing energy blasts, creating energy shields, and it even injects the user with a powerful stimulant which boosts their strength, speed and stamina- though it does tend to give new users delusions of grandeur. However, a season later, Crichton is trying to get help from characters he ran into during the first season, and naturally goes looking for the Tavlek mercenaries who use the gauntlet; unfortunately, the only one he can find has found religion and refuses to help, so Crichton just finds the gauntlet and decides to wear it himself... only to recieve a curt warning that the stimulant dosage has been boosted- enough to kill him in about three hours.
 * In Super Robot Red Baron, the titular giant robot has "Baron Full Power", a last-resort attack mode that uses all of its power reserves. However, if it's used for longer than one minute, Red Baron will explode(!)..
 * In the same vein as Red Baron, the Karakuri Giant Senpuujin of Ninpuu Sentai Hurricanger has a Super Mode called Hurrier Mode, which sheds its armor and allows it to be faster and agile for sixty seconds. If it doesn't revert back within that time, it'll suffer internal damage.

Live Action Film

 * In 90's Godzilla films the king of the monsters can fire a much stronger version of his blue atomic beam that is red and has lightning spiral around it if he absorbs enough energy. The down side is if he absorbs too much power he will turn into a meltdown mode that will cause a Superpower Meltdown that can burn up the atmosphere and kill all life. In Godzilla vs. Destoroyah, he does end up going into meltdown mode.

Tabletop Games

 * One of the mutant powers in Paranoia is Adrenaline Control, giving the character superhuman strength by having his body working at maximum capacity. This is never a good thing: "he's Superman for a minute, but...pays for it."
 * A supplement for the Mutants & Masterminds system includes a drawback (though how much of a drawback it really is is contested) called Holding Back. When triggered, the character in question gains a huge power boost, but side effects range from attracting attention from powerful enemies to going berserk on your allies to becoming comatose afterward.
 * The Complete Mage supplement for the 3.5th Edition of D&D features the spell "Transcend Mortality" for the Wu Jen. It gives DR 30/epic, SR 21+CL, resistance to all five energy types, immunity to abilitiy damage/drain/disease/poison/death effects, and negates your need to breathe. The catch? The spell lasts for roughly 2 minutes (depending on the mage's level), after which you immediately die and turn to dust. Said death cannot be prevented by any means.
 * As with all things D&D, this can be made into a Game Breaker. The Spellguard of Silverymoon learns to cast spells on nearby others that normally only work on themselves. And Transcend Mortality can be dismissed by the caster at any time.
 * Also, while Death Is Cheap by the time you can use it, only four very, very powerful spells can bring back someone who has been turned into dust. Namely:Wish, True Resurrection, Contingent Resurrection (which is an Epic level spell), and Miracle.(although you can create more epic spells to resurrect someone from such a state)
 * AD&D incarnation of Leanan Sidhe (see above) -- a vampiric spirit who charms bards, inspiring, and boosting their abilities, but gradually draining hit points (permanently).
 * Rifts has two classes that fall under this trope.
 * The first are Juicers. Chemicals (and nanomachines) are constantly pumped into a human to turn them into a superhuman - but at the cost of burning out and dying after five years.
 * The second are Crazies. Instead of physical enhancement they go the mental enhancement route. This gives them incredible psyonic powers, but again, at the cost of burning out and losing all sanity.
 * Changeling: The Dreaming used Leanan Sidhe to create a whole house of Sidhe who did just that - and a game mechanic for all fae to do the same.
 * Eversor Assassins in Warhammer 40000. These drug-crazed killing monsters are called the Latin word for 'Destroyer' for a reason, enemies (or walls) don't last long when they are around. Eventually all of the genetic alterations, combat drugs, and bionics with which they are equipped overwhelm their hyperactive immune system and they overheat rather explosively. The only thing that keeps them alive between missions is that they are kept in cryogenic stasis.

Video Games

 * In Baldur's Gate 2, the PC is granted the ability to assume the form of the Slayer, a manifestation of his dead father Bhaal, the God of Murder. Not only does maintaining the transformation kill you, using it is an inherently evil act that lowers your reputation, and may cause you to turn on party members.
 * It also isn't much of an upgrade, seeing that you can't cast spells in this form, and if you're a combat class already, can actually make you less formidable. However, it does come with no small amount of side benefits, such as immunity to many powerful nuisance spells, and as such for many characters is the tactic of choice for fighting certain creatures, like demi-liches.
 * It also opens magically locked doors.
 * Berserkers in Dungeon Fighter Online get the Frenzy skill, which more or less makes them Bloody Murder Personified (blood weapons, Blood boost), but drains health over time. Though use of HP regeneration Avatar items can slow the process.
 * The Berserker skill, Thirst, qualifies as well (only in the Korean version at the moment). At a cost of 12 percent of the berserker's max HP, bleeding damage is significantly increased, certain skills do more damage, and the berserker can absorb more HP from his slain enemies. This, combined with Frenzy, makes the berserker's HP unstable as it's constantly shifting upward or downward.
 * Front Mission 3 had the Imaginary Numbers and Real Numbers, groups of genetically engineered individuals to gain extraordinary abilities, such as reaction time, piloting ability, or tactical knowledge. The Imaginary Numbers were insane to start with, but both they and the Real Numbers got significantly less stable as they used their capabilities more until the individual eventually snapped.
 * Front Mission 5 applies this trope in a similar fashion. Certain individuals have Type S devices implanted in their brains, which give super-human reaction times and allow some pilots to interface directly with specific mecha. Such devices aren't without cost, though: those so enhanced lose portions of their memory and even basic functionality, with even the best-case results losing upwards of 20% of their memory.
 * In Castlevania: Portrait of Ruin, it is revealed that the Vampire Killer whip drains the life force of any non-Belmont who uses its true power. Jonathan Morris is warned against relying on it too much. Luckily for him, though, it takes longer than covered in one game to kill you...
 * Also, in Order of Ecclesia, you can get an item called the Death Ring. It boosts all your stats by a considerable amount...at the cost of you effectively becoming a One-Hit-Point Wonder.
 * There are also the Dominus Glyphs. Using one deals tremendous damage, and at the same time takes off a sixth of your HP.
 * Not to metion using the Dominus Union. It will kill all enemies on-screen This later becomes
 * The dragon transformation in Breath of Fire: Dragon Quarter results in rapid accumulation of points on the D-Counter, which constantly increases at a much slower rate, cannot be lowered by any means, and results in a Nonstandard Game Over when it hits 100%, strongly discouraging you from using it at all.
 * Similar deal in Breath of Fire III with the Kaiser dragon form. It's Ryu's most powerful dragon form, but the first version you get you can't control Ryu when he uses it. You can however, get a controllable version.
 * Earthbound has the party
 * In the Heaven's Feel route of the Fate/stay night VN, . It is wrapped in a cloth that seals its power, but even if left like this, it would kill him from power overload within ten years unless he . Just loosening the cloth causes significant memory loss; taking it off completely is a guaranteed death sentence, with rapid destruction of mind and body on top of that with every use.
 * In .hack, Kite has Data Drain, which weakens enemies to the point where they can be taken out with a single hit. But using it can result in level and stat reductions or an instant game over. He gets an upgrade that allows him to use it on multiple targets and yet another that increases the chance of getting a rare item, but both increase the likelihood of negative effects occuring.
 * In the video game Haze you have access to a super-drug called Nectar which gives you enhanced speed, accuracy, and grenade range, but overdosing could result in losing control of your character or even death.
 * In Crimsonland you can activate the Death Clock perk which gives you 30-second invincibility... After which you die.
 * A central point of Metroid Prime 3: Corruption. Samus gets a powerful "Phazon Enhancement Device" added to her suit that allows her to transform into a hyperactive killing machine, but over-use of it will cause her to become 'corrupted' and end the game.
 * And even if you don't overuse it, it'll probably kill you anyway - witness the PED-equipped Marine with the suspiciously shaky hands in the Preview Channel video, to say nothing of


 * And in a moment of Fridge Brilliance, using the PED also explains why the Space Pirates' experiments with Phazon frequently caused Unstoppable Rage: Firing indiscriminately is the easiest way to get rid of excess Phazon, preventing an overdose.
 * In Luminous Arc III receives one that greatly powers him up, at the expense of losing his humanity every time he uses it, starting with his senses. Surprisingly enough it is strongly impled that he
 * Debatable as some ending implied that he has.
 * Used in Kingdom Hearts II with Anti-Form. Engaging a Drive form (other than Final Form) has a chance of instead turning into Sora into something akin to The Heartless (suggested to be his connection to ). Anti-Form is completely unable to gain experience, and it's completely unable to recover health. Slightly related to both, it's also the only form that Sora can't cancel partway through. It's not bad if you're just starting against a boss, and at full health. But if either recovery or experience points are in the coming, you will be affected by the downsides.
 * And naturally, it is much more likely to pop up in battles with Organization XIII members, many of whom are the bosses you most need healing and damage resistance for.
 * In Prince of Persia: Warrior Within the Prince at one stage Under the circumstances, you need it.
 * This doesn't quite count as the Sand Wraith's health does not drop below 25%.
 * In Prince of Persia: The Two Thrones at certain points, the Prince transforms into the Dark Prince, who is faster and stronger, but cannot use his left hand for grappling or picking up weapons, instead he has a spiked chain-whip. In addition, he slowly loses life to the darkness, which can be replenished by absorbing Sands of Time. He reverts back to the original Prince if he touches water.
 * In Prince of Persia 2: The Shadow and the Flame, transforming into the Shadow shortens your life meter by many potions, and using the Flame costs further health. Both are necessary to defeat the Final Boss.
 * One mission in Devil May Cry 3 has Dante acquire a key needed to progress to the next area. Said key drains the soul of the bearer, and he can't let it go until he reaches the area it's used. Of course, sticking around too long without health refills will eventually kill him. To give Dante a fighting chance, the key also allows him to be in Devil Trigger form permanently.
 * This is an echo of a mission in the original Devil May Cry, which carried all the same consequences for waiting around along with the same perpetual Devil Trigger benefit.
 * Rampage Mode in the Oneechanbara series, a product of the Baneful Blood carried by most of the playable characters. Their offensive abilities are greatly increased, at the cost of taking double damage and constant health drain. There's also a Double Rampage Mode which is even more powerful and even more deadly.
 * Valkyrie Profile Covenant of the Plume has the titular Destiny Plume - when used on an ally, it multiplies their base stats by 10, makes them immune to status aliments and elemental damage and uses an extremely powerful character-specific ability The Hero learns permanently after the battle, but it costs them their life at the end of the battle. It could almost count as a Heroic Sacrifice, except the choice is never theirs to make.
 * At the end of Indiana Jones and the Fate of Atlantis.
 * Age of Wonders: Shadow Magic has Martyr enchantment: it doubles one unit's HP, but this unit dies once the battle ends.
 * Rugal Bernstein of The King of Fighters acquired some of the Orochi power after '94, becoming Omega Rugal. The problem is that those without the Orochi bloodline have no way of controlling it. After his defeat in '95, the power overloads and reduces him to his component atoms.
 * Mission Critical featured the Hype/Telecon System, which allowed the player to control the ship's combat drones with his mind. Unfortunately, the nanotech injection required to take advantage of it would cause certain death within a few days.
 * And then uses it again at the end. Supposedly, allows him to survive.
 * In Tsukihime even before the story starts, Shiki had the Mystic Eyes of Death Perception activate, greatly supplementing his killing power. Obviously. Of course, it burns his brain out and he'll die in ten years or so but... Also when he overtaxes even that in order to see
 * The Nasuverse really likes this trope, doesn't it?
 * If the cute bunny creatures in Cave Story consume the red flowers, they transform into GIANT, VIOLENT KILLER RABBITS!
 * If it isn't clear why this is a problem, the catch is they can't change back. They basically become giant, violent, killer rabbit berserkers until they get killed, in combat or old age or whatever. They do turn back to their original forms after dying, though.
 * Ragna the Bloodedge from Blaz Blue has his Blood Kain mode, which improves the properties of his Drive attacks and allows him to use the Devoured by Darkness Distortion Drive, but it saps his HP while active. And since he's a Glass Cannon already without it...
 * Command & Conquer III: Kane's Wrath has something like this the Steel Talon subfaction has two of these. The first railgun accelerator support power. It increases rate of fire of a unit that a railgun, but they take damage when it's first cast them. Not too big of an issue because the Steel Talons can easily repair their vehicles. They second is the adaptive armor support power. It makes a vehicle more durable grants it immunity to EMP weapons (very good for an epic unit because EMP weapons are of the main counters to them), but lowers their rate of fire. Can be remedied with the railgun accelerator if the unit uses railguns. Common strategy is to use both on the unit an enemy concentrates fire on at the start of battle.
 * Battle Clash and Metal Combat: Falcon's Revenge have a power-up called the V-System, which increases your offensive ability and always keeps your opponent centered within your sights. In order to power this, however, your mech's energy gauge is continuously drained until you reach critical.
 * It's not quite deadly, but the Mega Mushroom in New Super Mario Bros has the side effect of returning you to Super Mario form when its period of invincible Attack of the 50-Foot Whatever wears off. Thus, if you picked it up as Fire or Blue Shell Mario, it has the net effect of stripping Mario of one of his maximum three Hit Points.
 * In the web-only game KOLM, the final upgrade you receive.
 * In BioShock (series), the first Plasmid power you recieve causes Jack to temporarily go mad and black out.
 * In one mission of Assassin'sCreed:Brotherhood you get to use
 * Persona 3 has this in spades. First, many Personas learn physical attack moves, but using them drains up to a fifth of the character's HP.

Web Comics

 * Problem Sleuth gained wings, glowing armor, superpowered weapons/writing implements, and access to insanely potent attacks upon using Sepulchritude, however, once his Ink of Squid Pro Quo (which powers Sepulchritude) ran dry, he was left helpless, nearly paralyzed and at the brink of death.
 * In the webcomic Mindmistress, the title character uses a piece of Applied Phlebotium that grants her Braniac-level intelligence. But if she leaves it active for too long, it will leave her with brain cancer, if not killing her outright.
 * Similarly, Dauntless, a super-hero imbued by her, must detransform periodically or his enhanced nervous system will cause him to overload on sensory input.
 * Noetic Chiasm's Meristogenous Transgression was developed by Meander, the main character of 10%+, to help counteract his tendency for his mind to wander; it allows him to focus his full attention on multiple things at once (which proves very handy during his battle against Rule). Downside? Putting that much stress on his mind will (and does) cause brain damage.
 * In Girl Genius Smoke Knights sometimes use combat stimulants. A severely wounded subject under Movit #6 can run around and fight, grinning maniacally for a few hours. Movit #11 "would kill almost anyone" on its own.

Web Original

 * Recoil from the Global Guardians PBEM Universe had the power to absorb electromagnetic energy and use it for his own purposes. His absorption had no upper limit, but the more energy he took in, the more damage he suffered. When Doctor Devastation unleashed a superweapon that used an electromagnetic signal to trigger autosuicide in some 30% of the human population, Recoil wrapped himself around the broadcaster and set his absorption power to "Go Ahead And Kill Me, But I'm Stopping The Signal." And he did. And it did.

Western Animation

 * On Justice League Unlimited, The Flash goes really, really, really fast, and ends up nearly pulled into another dimension, communing with a quasi-mystical "speed force," one of the show's many Shout Outs to the comics.
 * One episode of the Men in Black cartoon had Agent Jay accidentally use an intelligence-improving device that would eventually cause his head to explode. After using his new brain to help deal with a time-traveling villain who was erasing the founding members of the Men In Black from history, Jay managed to deal with this by hijacking the baddie's time machine and preventing it from happening in the first place.
 * In the second season finale of WITCH, the heroines must unleash "their dragons within", literally becoming the elements water, fire, earth, air, and quintessence. Because water, fire, earth, air, and quintessence aren't human, the girls lose their humanity as a consequence, and must be brought back to normal by their loved ones after the end of the fight.
 * In Transformers Animated,
 * Avatar: The Last Airbender has this with the Avatar state. It's a Powerup Mode that gives the Avatar the combined skills of all the previous Avatars, making him/her nearly invincible. Downsides are that it's hard to control without training (very bad since it turns the Avatar into a Person of Mass Destruction), and if the Avatar dies in the Avatar state, then the Avatar's cycle of rebirth will end and the Avatar will cease to exist.
 * Beast Boy from Teen Titans transforms involuntarily into The Beast in the episode "The Beast", which he from then on is able to become at will. Said beast is incapable of higher thinking and liable to attack the other Titans, but possesses strength beyond that of his teammates and Super Speed.
 * Danny Phantom uses the ecto-skeleton in Reign Storm to defeat Pariah Dark (and it is AWESOME), but at the cost of 95% of his life energy. He gets saved just before burning through the last of his energy by Vlad Plasmius and every other ghostly opponent he ever had.

Real Life

 * Anabolic steroids are well known for their ability to make us harder, better, faster, stronger, etc. The downside is that there are a HUGE amount of side effects, not the least of which are heart problems, cancers, "roid rages," and man-boobs.
 * Sometimes Truth in Television. Not all anabolic steroids and analogues are all that dangerous when taken in controlled amounts (assuming they're pure, and illegally-obtained drugs often aren't). Others are suffering in liquid form, inviting the physiological side affects mentioned above and others, as well as significantly increasing the risk of manifestation of psychological disorders in those with pre-existing conditions.
 * The vast majority of psychostimulants leave the user in a "smoking ruin" state by the time they wear off; mostly due to straight metabolical overload, so the more performance enhancement given, the more damage caused (usually not permanent). Exclusions (like Eleutherococcus group) works by rising power throughput and more adaptogenic with useful side-effects than stimulating.
 * Not to mention adrenaline. The flight-or-fight system normally doesn't pump enough of it to harm your heart or body, usually. However combine it with certain Heart conditions (like Broken Heart condition) and your heart will not surivive. Outside sources of Adrenaline, if not in a controlled will cause your BPM (Beats Per Minute) to skyrocket and cause a heart attack. And this isn't even getting into adrenal disorders like Adrenaline Overload (as some doctors call it), which is basically the flight-or-fight system activating randomly and not turning off for a while.
 * Adrenaline's pain killing properties, and its "tunneling" of sensory perception can also lead to people injuring themselves much more often then usual. This is considered "worth the risk" from an evolutionary standpoint, as there is little substitute for the quick decisive reactions of the fight or flight response in many cases; unfortunately, seeing that the conscious mind cannot control the flow of adrenaline, people often enter the fight or flight response when it is completely inappropriate for the situation, with potentially harmful results.
 * Also, increased strength from adrenaline rushes (like a mother lifting a car off her child) is capable of causing serious damage to the body. The muscles, tendons, and ligaments aren't built to take a beating like that on a regular basis, which is the main reason your body only allows superhuman feats of strength under the most necessary conditions.
 * The body uses another steroid, cortisone, to reduce inflammation and pain, which it does by suppressing the immune system. It is primarily released during periods of stress, which accounts for consequent illnesses. And any pain inhibitor in general is risky, as pain normally prevents someone from causing injury to themselves.
 * This is likely the cause of what most students experience in the form of the post-finals flu.