Improbable Antidote

Oh no! Bob was just given an injection of Killsyoucine, the most deadly poison known to man! He's doomed! Wallowing in despair, he gorges himself on pop-tarts to drown out the pain...

...but wait... why is he feeling better?

Poisons come in all sorts of forms. So do, it seems, antidotes. Anything might turn out to be one! Often, the poisoned is not aware of the antidote until after it's been ingested, but in any case, rest assured that it won't be the last time it comes up.

Anime and Manga

 * In Detective Conan, Conan is given a kind of Chinese alcohol called baigar for his cold. This leads to the discovery that
 * In the Galaxy Angel manga, Chitose (under a very complex example of Brainwashed and Crazy) uses a special poppyseed to poison the entire Angel Troupe. After escaping and kidnapping Tact, it turns out that the antidote was an uncommon spice - that happened to be in the fried chicken Milfeulle had just made and they had all been eating. (In spite of one of the group supposedly being a religious Vegetarian.) Milfie's power is extreme luck, though, so...

Comic Books

 * In the Marvel Transformers series, Blaster and Bumblebee, along with baddies Blitzwing, Astrotrain, and Octane, are infected with robo-parasites known as Scraplets.  The only cure: an extremely rare chemical compound. If they can't find it, goodies and baddies alike will have to be dissolved to stop the potential epidemic from spreading.

Film

 * A supernatural example comes in the Ring movies, where the female lead does the thing to break the curse, without knowing it.
 * In the movie Almost Heroes, Chris Farley must find the Egg of an Eagle to save Matt Perry. Hilarity ensues after his repeated assault by the eagles and falling out of a tree keep breaking the eagle's eggs. Finally, he brings the last egg, intact, back to the camp, only to find out that the antidote is the egg shells.
 * In the Steven Seagal movie The Patriot, the cure for the bioweapon the villains released turned out to be the herbal tea that the hero and his daughter had with breakfast the morning before they were exposed to the virus.

Literature

 * A Series of Unfortunate Events, where the antidote to the deadly mushroom, the Meducoid Myceclium, turns out to be horseradish (can be substituted with wasabi).
 * Sort of used in one of the Temeraire books; while, Temeraire unknowingly ingests the curing in a chef's experiment.
 * Subverted in Vigilant. The scope of a plague (later revealed to be a bioweapon) becomes so large and devastating that medical science gives up on trying to find a cure the normal way and ends up trying whatever random thing comes to mind. The cure is found to be olive oil...subverted, because it much later turns out that someone developed the cure, and then altered the olive oil to carry it, unknown to anyone at the time.
 * The Rowan of Rin series did this with one of the fish-people tribes having created one hundred poisons and an antidote for each. The one that poisons his mother had a very strange antidote, which that last of the antidote had been used up. One handful of silver sand that can only be found in a pool of water that has carnivorous fish, the juice of a flower that grows underwater in that pool, a fresh feather from a monstrous bird that hunts the fish, and, the best one, a drop of venom from the sea serpent queen that crawls onto land to that pool just to lay her eggs in the pool once a year at that particular day that his mother was poisoned. At least he was given the recipe beforehand.
 * In Vertical Run by John Gilstrap, the hero has a disease throughout the story that's progressing. At the end, after thwarting whatever evil scheme was afoot, he accepts his fate and goes to the mountains to spend his last days.
 * Holes deals with a particularly deadly lizard with a particularly deadly poison.
 * The Andromeda Strain causes instantaneous and lethal blood coagulation throughout the body. It also
 * Book Four of The Hitchhikers Guide to The Galaxy contains an off-hand mention that Arthur's lunch when he first gets back to Earth (which consists of the three least mouldy things in his fridge) actually cured him of a space-disease he'd unknowingly picked up which, uncured, would have killed or rendered infertile everyone on the planet.

Live Action TV

 * In the Doctor Who episode "The Unicorn and the Wasp", the Doctor cures himself of cyanide poisoning by covering himself in ginger beer, eating walnuts and anchovies, and getting kissed. Don't ask.
 * Justified by the Doctor's well-known Bizarre Alien Biology. Not to mention the Rule of Funny.
 * An interesting usage by House, as well as an example of Truth in Television. One episode featured a death row inmate who has tried to kill himself by drinking several bottles of copier fluid. House sits by the guy's bedside as his poisoning worsens, and the two of them each down several shots of high-proof rum. Only after a while does House reveal the truth: copier fluid is about 90% methanol, or wood alcohol, and the treatment for that is large amounts of ethanol, or grain alcohol. All those shots he had the guy drinking were slowly curing him.
 * An episode of MacGyver had Pete poisoned by prussic acid (Hydrogen Cyanide) gas in a mall. Mac recognizes the poison by its distinctive almond smell and dashes toward a photo developer booth, whose printing machine contains Sodium Thiosulfate, an antidote for cyanide poisoning.
 * An episode of The Invisible Man series was centered on quicksilver-producing bacteria, which had eventually proven to be lethal. At the climactic moment, the cure was conveniently found... in mayonnaise.
 * BAD mayonaise to be specific, they realized it when one character who they had presumed was sick like everyone else turned out to just have food poisoning from his favorite lunch place. The bacteria in the food out-competed the quicksilver-producing bacteria, essentially saving everyone's lives by making them puke out their guts.
 * In the 2006 Robin Hood series second season episode had the town being poisoned by the Sheriff. Once the heroes know what the origin of the poison is, Little John realizes the cure is giving the people the dangerous herb belladonna, aka Nightshade.

Video Games

 * The Lamasu coming in Might and Magic: Heroes 6 will have some sort of a poison or disease effect - with them themselves being a result of failed experiments on manticores, then made undead by the necromancers to counter the short lifespan and fragility of living results. The poison effect will persist through a battle, but be cured as soon as the battle ends. The Hand Wave given by the developers? The soldiers need to just take a short nap to be cured. Also counts as an Universal Poison, as it can affect various breeds of demons, humans, and hybrids (acting as greenskin) alike.

Western Animation

 * A variation occurs in The Secret Show, where the entire population of Helsinki is forced to hate Victor Volt and Anita Knight, the protagonists. The cure? A batch of chocolate chip cookies Professor Professor made that turn a consumer's head into a balloon for a maximum of 2 hours, 30 minutes, and 10 seconds.

Real Life

 * Warfarin is a substance used as a rat poison. The antidote is vitamin K, commonly found in all fruits and vegetables, but parsley has the highest content-per-weight. So, parsley is the antidote for rat poison. Warfarin is also used as an anticoagulant, and people who consume warfarin for this reason are told to stay away from vitamin K-rich foodstuffs.
 * Atropine (from deadly nightshade) is a lethal poison, but is also the antidote for nerve gases such as tabun. The reason being that they affect the nervous system in opposite ways, so they cancel each other out.
 * Neither of them is good for you, anyway, and contrary to the way it's depicted on-screen someone who's been exposed to nerve gas and atropine is likely to have severe neurological damage. This is better than someone who's been exposed to nerve gas alone - who is usually just dead - but not by much.
 * Ethylene glycol (frequently used as antifreeze) is moderately toxic. It's toxicity is mostly due to its metabolites, so the treatment is to saturate the enzyme that breaks it down with ethanol. Usually, it's administered intravenously, but if necessary it can be administered orally (as vodka, whiskey, or another strong spirit).
 * Under certain circumstances, alcohol can be a quite effective treatment for radiation poisoning. While not an actual antidote, the alcohol molecules bind the particles of a certain isotope that then leaves the body along with the alcohol via digestion. It works on the same principle as iodine tablets, but when you don't have any at hand, strong vodka will also reduce the effects to some degree.
 * In the wake of the Chernobyl meltdown, vodka fortified with iodine and sold under, among other names, Doktor Vodka became very popular among those who lived near the plant.
 * Wait, so the Soviet Union experiences the worst nuclear plant disaster in history, and the cure is heavy drinking? Does that count as amazingly bad luck, or good?
 * Before the discovery of vitamins, fresh foods (especially citrus) as a cure for scurvy and other deficiencies.