Medicine is hard. You have to diagnose people's illnesses, run tests, and prescribe treatments. But what if you could just give out a one-size-fits-all treatment? There are lots of miraculous panaceas in science fiction and fantasy, which can fix any problem. Here are the five types of fictional miracle cures.
The prevalence of easy cures for any ill makes total sense. It can stop storytelling in its tracks to have to explain every illness or injury and the various associated treatments. If that's not central to what's going on, just hand them something generic to fix it and send them on their way. So here are the five types of cure-alls and where you can find them.
Some cure-alls literally grow on trees. In Middle Earth, there is "Kingsfoil," the plant Aragorn puts in that Nazgul-made hole in Frodo. It's used to heal wounds after the Fellowship goes through the Mines of Moria. And Aragorn uses it again to heal Faramir, Eowyn, and Merry from the Black Breath.
In The Mallorean by David Eddings, a flower created by magic has the power to heal contained in its scent. And there are apples in Narnia that can cure disease, so long as you harvest them for another. Trying to use them for yourself will not so much heal you as curse you.
Other sources: The Lansip Fruit in Tales of Kolmar by Elizabeth Kerner, the "Blessing of the Night" mushroom in Codex Alera by Jim Butcher, the mushrooms in Super Mario Bros.
Magical artifacts can also be sources of cure-alls. The Philosopher's Stone is often described as healing all forms of illness and prolonging life. The legend often requires parts of it to be ingested for it to work, so it's not an infinite resource. In Harry Potter, Voldemort seeks it to restore his body (and escape a life under Professor Quirrell's turban). This kind of use of the stone also shows up in The Alchymist's Cat by Robin Jarvis, the manga Busou Renkin, and a number of video games. It's more popular in storytelling for its other skill: making gold.
Other sources: The Elenium by David Eddings has the "Bhelliom," a magical sapphire carved in the shape of the rose, which is the only thing powerful enough to cure a certain poison. Plus the Resurrection Stone in the Marvel Universe
This is another one where Voldemort comes in. In Harry Potter, the blood of unicorns will keep someone alive, even if they are "an inch from death," but it'll also curse you. Voldemort uses it as a stop-gap measure on his way to getting the Philosopher's Stone. In Final Fantasy, the Phoenix Down, made from the bird's feathers, brings people back from the dead. It's also described as being a cure for "undeath," which is a nice bonus.
Other Examples: Phoenix tears also serve as an antidote and healing potion in Harry Potter.
When there's no plant, magical artifact, or piece of a mythological creature nearby, it's technology to the rescue. The Stargate Universe's Goa'uld took on the personae of Ancient Egypt's pantheon, so it makes sense that they'd also package their life-restoring technology as a sarcophagus. Note: While it works really well on the body (to point of bringing you back from the dead), repeated use has the slight side-effect of making you evil.
Other examples: The nanogenes in Doctor Who's "The Empty Child"/"The Doctor Dances," a device that restores full health in Larry Niven's Known Space, the mind transfer technology in Lord of Light by Roger Zelazny, cortical stacks in Takeshi Kovacs by Richard K. Morgan, consciousness transfer in Old Man's War by John Scalzi,
This is the biggie. The multiverse is replete with pills, syrups, injections, and gels that will heal anything, from a stab wound to the flu.
Star Wars has bacta, which basically ended medical research in that universe. Because why look into other cures when you've already invented a substance that heals everything? (Because it's made on a single planet that is, apparently, pretty conquerable?)
The Andromeda Strain by Michael Crichton had Kalocin, a wonder-drug effective against all viruses, bacteria, parasites, funghi, and disease generally. It's so good that the human body refuses to compete with it, shutting down its own immune system.
Other sources: Aqua Cure from Resident Evil, Ascomycin from Cities in Flight by James Blish, Celestial Wine from the RPG Exalted, Elyon’s Water from The Circle Series by Ted Dekker, Ether from Final Fantasy, Interfectum from Max Payne, Lazarus Pit from thr DC Universe, Medi-Gel from Mass Effect, Mono/Di/Trimate from the Phantasy Star Series, Regen therapy from the Honorverse by David Weber, Selenine from The Plutonian Drug by Clark Ashton Smith, the Senzu Bean from Dragon Ball, Stabilization Serums from the Gor series by John Norman.