This Is Your Brain on Evil

""Sanity... is for the WEAK!""

- Various followers of Chaos, Warhammer 40,000

"You think I've not tried to stop - to stop tying? I'm hooked! It's a habit with me now! Oh, boo-hoo-hoo! I swear to you: after I tie up this one defenseless woman, I'm going to swear off, so help me!"

- Snidely Whiplash, Dudley Do-Right

So you've just performed a Face Heel Turn. Maybe you gave in to your Super-Powered Evil Side, or you experienced a Freak-Out, or you have your first shot of real power and see what having such control and influence can get you in life. Whatever the case, you've just taken your first taste of the true joys of evil, and it tastes good. You become enthralled, never turning back to your old ways (and shun off all attempts by your friends to do so), and are living the high life, loving every sadistic moment of your new existence.

Then, you feel it: a straining in your head, a dagger-like pain in your chest, a feeling of queasiness or disorientation or some other physical malady. Or you realize you've become incredibly cold and antagonistic toward your friends and loved ones, followed by a feeling of being out of control with your own actions. Something is wrong; you never expected this to happen. And if you don't find a way to stop it, it'll ruin your relationships, kill your career, or—in the most extreme cases—drive you into an early grave.

Congratulations, This Is Your Brain on Evil. Since evil is often depicted as being a tantalizing and corrupting influence, it's just as often used as an euphemism for another, similarly tantalizing and corrupting, influence: drugs. And, just like drugs, the side effects are all there: addiction, withdrawal, uncontrollable behavior and, eventually, health problems and death. Usually, when a character is thrust into this trope, they get into it only knowing or caring about the positive, "feel-good" parts of the power or evil they're taking and never seem to realize that they can't take the "good" parts out of the deal without acquiring the negative as well until it's almost too late. Once they reach that point, they're almost guaranteed to try to "quit" their newfound lease on life to ensure that it doesn't destroy them and those around them completely. Sometimes they succeed, sometimes they end up dying and regretting having ever started in the first place.

When it's well executed, this trope can go a long way toward taking the romance out of evil and making it more frightening and personal. When it's done badly, it's a heavy-handed Aesop on the dangers of giving in to temptation and getting involved in something you really shouldn't have.

The trope's name comes from a series of anti-drug public service announcements in the 1990s, using an egg pre- and post-cooking to demonstrate a person's brain pre- and post-drug burnout.

Contrast Evil Is Cool and Evil Feels Good. Compare The Dark Side and Evil Is Not a Toy. Also see Drunk on the Dark Side

Anime and Manga

 * Ryo/Kaiser in Yu-Gi-Oh! GX started coming down with life-threatening heart problems after his Freak-Out and Face Heel Turn. At first, it was assumed that it was because of the electroshock collars he became addicted to during his tour through the Underground Duels, but later it was revealed to be a result of the dark power of his own "Underworld Deck", which he forcefully acquired from his old mentor and relied on for most of his villainous career.
 * In the Chaos;Head remake's route for, the lead female winds up pulling a This Is Your Brain on Evil and an Evil Feels Good simultaneously. Naturally, it gets worse.
 * If you think that Light Yagami is capable of maintaining his sanity after he starts writing names in the Death Note, you haven't been watching or reading the series anywhere near close enough.
 * Pretty much applies to any Kira, in particular, Mikami and (in the films) Takada.
 * The Giant Sakura Tree in Da Capo essentially does this to Sakura by granting her subconscious desires even when she begs it not to.
 * Most characters in Soul Eater who go through a Face Heel Turn starts to suffer from quick deterioration of their mental faculties soon after, which is not at all surprising, considering that a Face Heel Turn in this series usually means giving in to insanity. Examples include  in the anime;   in the manga; and, obviously, Kishin Asura in both.

Comic Books

 * During the Alien Costume Story Arc, Spider-Man becomes addicted to the power and freedom the Venom symbiote gave him... until he learned that it exacerbated his aggressive tendencies and would've absorbed him into itself in the long run. Peter Parker managed to "quit" the symbiote, but his successor, Eddie Brock, wasn't so lucky. Note that this wasn't actually a part of the original comic-book version, but has appeared in all the adaptations.
 * Brock seems to be better, now. At the moment. Sort of. Meanwhile, under the Symbiote's influence, Mac Gargan has crawled up the food chain of evil, in more ways than one.
 * The Sonic the Hedgehog Archie comic delved a little into this with the Chaos Emeralds. Knuckles' ancestor Dimitri, who would later become the power-mad Enerjak, got hit with the "withdrawal" symptoms of this trope once his Enerjak powers were removed; rendered unchanged by his powers for centuries, their sudden absence quickly reduced him to a frail old man on the verge of death, forced to live on cybernetic means for the rest of his life (and in one possible future, being reduced to a head in a jar).
 * Similarly, in a (now non-Canon) future, Knuckles gets juiced up on Chaos power and goes mad, attempting to reshape his world as he sees fit. He was stopped by Sonic and an alien device, but it robbed him of an eye and all but irreversibly annihilated his relationship with the hedgehog. Note that canonically, he's already been pumped up with Chaos energy once, and while he didn't go insane or anything, he still died (he got better, though).
 * This actually sort of happened in a recent arc with Knuckles being taken over by the Enerjak power- however it ended better with Sonic forgiving him, though Knuckles still feels bad about it.
 * Some incarnations of Super Sonic are treated this way, with Sonic usually trying to find a way to subdue his Super-Powered Evil Side.
 * In the Emerald Twilight arc of Green Lantern, Hal Jordan starts out slightly unbalanced with grief over the freaking demolition of his home city and after a minor nervous breakdown, charges out towards Oa to call out the guardians for their long-running history of being selfish assholes. However, he then starts robbing and killing all the other Lanterns who get in his way, and goes from "unbalanced" to "totally batshit insane" over the space of 22 pages. At the time of publication, it was more a Despair Event Horizon, but it was then retconned that Hal had actually been infected by a fear-feeding Giant Space Flea From Nowhere, meaning Hal apparently lost his mind as soon as he got corrupted.
 * 52 established that selling one's soul is not only addictive, but exponentially detrimental to it, lessening it's "value" with each trade.

Film

 * The Dark Side (yes, the original from Star Wars) tends toward the physical aspects of this, slowly twisting, corrupting, and generally uglifying its adherents. In the Expanded Universe, it's explained that Emperor Palpatine had to leapfrog from clone body to clone body as he grew more powerful, with each one disintegrating faster.
 * From the Extended Universe, the ultimate example. Jacen Solo: most talented Jedi of his generation, both in power and in philosophy, able to go past dark and light and see the true Unifying Force behind it. Darth Caedus: all the power of Jacen Solo, half the intelligence, and twice the paranoia. "His cape had betrayed him." Any questions?
 * In the Knights of the Old Republic video game series, being fully on the dark side causes Glowing Eyes of Doom, wrinkled skin, a change in underwear (to a black-and-red jumpsuit-like thing) and some NPCs comment briefly on your appearance.
 * Of course, if you were on the dark side and they commented on your appearance, the rest of their lives were generally very brief.
 * In the final volume of Dark Empire, Darth Sidious underestimates the Papa Wolf again.
 * In the second Spider-Man movie, Otto Octavius has an epiphany after getting knocked around by Peter, realizing that his arms have been manipulating him, and urging him to evil. Sadly, he was surgically fused with them and may have "died" because Redemption Equals Death.
 * Also the Venom suite in Spider-Man 3.
 * In Mr. Brooks, the eponymous Serial Killer uses Alcoholics Anonymous mantras to try to resist the urge to murder. It doesn't work.
 * Loki announces his arrival in The Avengers by wreaking some serious havoc throughout the rest of the movie, signifying a dramatic change from his previous appearance in Thor. But his mental change for the worse is accompanied by physical changes as well: his hair is even more stringy and mussed than usual, his skin is unnaturally pale, and his eyes are sunken to the point of appearing bruised.

Literature

 * The Lord of the Rings: Witness what hundreds of years of Ring-addiction did to Gollum, not to mention the Ringwraiths. However, Gollum's appearance may not be so much an example of what happens when you abuse evil, so much as what happens when you live for 500 years without eternal youth.
 * The Chronicles of Narnia: The Turkish delight the White Witch gives Edmund in The Lion, the Witch, and the Wardrobe works a lot like a drug—the post self-isolation, his siblings noting he doesn't look well, "the more he ate, the more he wanted to eat... and if allowed, would go on eating it till he killed himself."
 * Edmund's (soundtrack only) Villain Song from the 2005 film agrees with this interpretation, with such lyrics as "a life of treats might do me in/but I've got to get another taste" playing up the addiction/withdrawal parallels.
 * In the Shannara series, if not subverted, at least subdued, in the form of the druid Allanon (as well as his mentor Bremen, and successor Walker) who dared to use the Black Magic out of necessity. Villains used the same power, and it corrupted them. It corrupted Brin Ohmsford, too, until her brother saved her. The druids are different, though; they understand the Black Magic well enough to take this threat seriously, and use it with steadfast discipline and carefully prepared Heroic Willpower strong enough to remain good guys (at least insofar as they do what must be done to vanquish evil) throughout their stint of public service.
 * Guards Guards: Summoning a dragon from an unknowable dimension and guiding it around the city according to your will? Fun. Addictive, even. Said dragon learning to summon itself into your city and taking its revenge first and foremost on you - your mind, your consciousness, your future? Not fun. Sorry,
 * The Dresden Files has Black Magic. When using an evil magic belt in Fool Moon Harry notes that the effect is an amazing high along with the designed effect. The White Council views all Black Magic this way as well and they have a strict policy on what to do with its users.
 * The addiction metaphor is pretty obvious in The Strange Case of Doctor Jekyll and Mr. Hyde. The physical symptoms aside, Jekyll even says he be rid of Hyde any time he wants... but, of course, once he wants to get rid of Hyde once and for all, he can't. The more he takes the potion, the easier (and less painful) it is to transform into Hyde until it's impossible for him to remain as Jekyll. (Note that it is not the potion that is addictive but the freedom from all conscience and moral restraint.)
 * In Paradise Lost, although the Forbidden Fruit is not addictive, it does make you feel happy, invincible, horny, and leaves with you a What Have I Done-hangover the next morning.
 * In the Dungeons & Dragons Abyssal Plague novels,

Live-Action TV

 * Buffy the Vampire Slayer went full-out with the drug comparison when Willow slowly gets addicted to magic. She has to get pulled back from the edge a few times before it sticks, and in the meantime she's a wired sorceress with eyes dilated to the extreme.
 * More tamely, when Buffy gets enticed by the sheer fun of Faith's delinquent and irresponsible behavior, she winds up becoming idiotic enough to burgle a gun shop without any precautions whatsoever, and gets arrested.
 * The Dresden Files TV show, being based on the book series, has this. In one episode in particular, it shows the effects on three college students as they "rot from the inside."
 * Stargate SG-1's Goa'uld tend to suffer from an actual physical addiction with evil as the primary side effect: the sarcophagus, particularly demonstrated in Daniel's experience with it in Need.
 * The Tok'ra, an offshoot of the Goa'uld, refuse to make use of the sarcophagus no matter what. They believe it's a major reason why the Goa'uld are Exclusively Evil, and consider their own reduced lifespans to be a perfectly acceptable trade-off.
 * Sylar from Heroes. Especially in Season 4. It looks like he wants it to stick this time. (Last time, he gave up because Ma Petrelli's urging of his reform was based on a lie.)
 * Season 4 of Supernatural has Sam becoming addicted to demon blood to stop the Apocalypse; he knows he's damning himself, but doesn't expect to survive stopping the Apocalypse anyway.

Tabletop Games

 * Chaos tends to do this in Warhammer Fantasy Battle and Warhammer 40,000. Its effects are best summed up in five words, usually shouted: "SANITY IS FOR THE WEAK!"
 * Of course backing out really isn't an option once you start worshipping Chaos. Not only have you made deals with extradimensional demonic entities for your powers (and yes, they WILL come and collect), once you have been associated with Chaos (or knew someone vaguely associated with chaos, or lived in the same village as someone associated with Chaos) then chances are the good guys (such as they are) will also be trying to kill you. And no, "I've quit" will not be taken as an excuse.
 * God help you if you worship Tzeench, Khorne, or Slaanesh. Actually, God can't help you, because they ARE your god.
 * Khorne, being the god of slaughter and bloodlust, will turn you into a battle-hungry psychopath one way or another, whether you want to or not (and by that time you probably do).
 * Tzeench, the god of All According to Plan and Sorcery, will grant you uncontrollabe telepathy, constant whispering always in your head, and can make you SEE FOREVER. Few people remain sane.
 * And finally Slaanesh, god of pleasure and excess; by the time he/she/it is done with you, your senses will be so dulled and jaded that you will need to censored at least three times over to even chuckle.
 * Pft, what about Nurgle? He's probably the nicest, friendliest god in all of Warhammer (yes, even nicer than the "good ones"). Heck, all he wants to do is give you a hug and some gifts, and his worshipers even call him Papa! Of course his "gifts" are plagues so virulent that a single microbe can infect an entire world within a few days, cause your guts to bloat until they burst and you're dragging around your own intestines, infest you with hundreds of horribly pestilent insects, and may even turn you into a literal zombie. Before all of that, of course, you've gone so insane from the constant pain and suffering that when Nurgle says he'll relieve you of it if you worship him you happily take it up; he doesn't actually make you better though, he just makes you enjoy it, and now you want to share Papa Nurgle's gifts with everyone else..
 * By which point you've become ridiculously tough and more or less immortal and immune to pain, moreso than other Chaos mutants, so if you don't want to be pretty or fast (though the latter isn't necessarily ruled out), Nurgle's gifts are the genuine article. And you still get to have a decent social support network (for a strictly quality-oriented definition of "decent"), something the other 3 Ruinous Powers don't offer. All of this is not to say that Nurgle averts this trope, but he seems to be the best Chaos has to offer in Warhammer 40,000 by a considerable margin.
 * With Tzeench, he also gives you shapeshifting, and does seem to care about his worshippers to some extent, he even intervened to save the Imperium during the Horus Heresy! Really, Tzeench is unknowable. Nothing you can say about him is known for sure, and his followers seem less likely to commit travesties than other Chaos Gods.
 * Vampire: The Requiem has this as the weakness of the Ventrue clan. Every character, once they fall down the Karma Meter, needs to roll to see if they pick up a Derangement as part of sublimating the fact that they did something awful. Ventrue get a penalty to this roll, making them more likely to pick up Derangements as they do bad things.

Theatre
"Why this is hell, nor am I out of it. Think'st thou that I, who saw the face of God and tasted the eternal joy of heaven, am not tormented with ten thousand hells in being deprived of everlasting bliss?"
 * Apparently not even demons are immune to this, cf. Marlowe's version of Mephisto(in Faust):

Video Games

 * In Fable, indulging in evil acts eventually mutates your form into a smoking, horned, flies-buzzing-around-you Palpatine wanna-be, who frightens nearby villagers just by the mere sight of you. Like your other actions in the game, though, this is only a superficial change, and doesn't do anything to change the story or your character in any significant way.
 * Fable 2 introduces corruption and purity in addition to good and evil. As a result, it's possible to be pure evil, which results in a pale-skinned, Glowing Eyes of Doom appearance, or corrupt evil, which results in a demonic form, complete with horns and fissures of evil. However, despite your appearance, it's possible to be a Villain with Good Publicity if you play your cards right, and people will just LOVE that random demon walking through town.
 * The Dark Prince in Prince of Persia: The Two Thrones mates this with Super-Powered Evil Side; at first, the Prince sees the Dark Prince as an asset, but once he realizes the evil selfishness it embodies, he refuses to even listen to it (and you're unable in-game to switch to him after this point) until . Also, when the Prince changes into his dark persona, he loses health rapidly, necessitating the need to get rid of it.
 * In Baten Kaitos: Eternal Wings and the Lost Ocean,.
 * Iori (and Leona's) transformation into the Riot of the Blood state in The King of Fighters is preceded by dizziness, hazy vision (as they lose their consciousness), and finally, vomiting up blood. Unlike many other examples here, this completely involuntary.
 * Riku, in the first Kingdom Hearts game.
 * In Mega Man Battle Network, many Navis initially use dark chips to become more powerful, but soon become addicted to them and start suffering withdrawal without them.
 * This is shown in game as the use of a dark chip deducts one point from your maximum HP...permanently. Deep in the Undernet you bump into navi-shaped shadow viruses stated to be the ultimate result of a navi completely giving in to their addiction.
 * Kefka in Final Fantasy VI. Kefka was once a perfectly normal Imperial General, until he got his magitek infusion. The process was still experimental and eventually drove him so far off the deep end he ended up in the deeper end.

Web Comics

 * Not an example, exactly, but used in this Sinfest.
 * Parodied in this The Thrilling Adventures of Lovelace and Babbage (aka 2D Goggles) strip, given that for Ada, Poetry -> Evil.

Web Original

 * Post Face Heel Turn Madison Conner of Survival of the Fittest going from a (very) emotional girl just trying to survive and transforming into a sadistic psychopath with little to no empathy. There wasn't even a trace of Character Development, making it incredibly jarring.

Western Animation

 * Pleasure Island in the Disney version of Pinocchio, where bad boys are invited to do what bad boys love to do... until they learn too late it's a trap, and the island is magically imbued to turn them all into donkeys after a while; after they have thus literally made jackasses of themselves, they are sold into slavery. Fortunately for the title puppet, he and a few other boys manage to escape before the transformation fully sets in.
 * In Finding Nemo, the heroes run into a group of sharks who are trying to give up carnivorism in an AA-esque setting. When Bruce the shark goes into a feeding frenzy after smelling blood, it's treated like a relapse (the other sharks even call it "falling off the wagon.")
 * One of the quotes is from the Dudley Do-Right segment of the Rocky and Bullwinkle Show

Parents, talk to your children about using evil. They'll listen...