There are several cures for the transformation of humans into various beings and the effects of certain curses and weapons.
Killing the Thule who cast the toxic spell will stop it.
Using a ritual created by Father Max Thompson involving injecting doses of purified blood and a modified exorcism can change a demon back into a human. This is referred to as "curing a demon." The second time it was done successfully was when Sam used it to cure Dean.
Generally, djinn poison is treated by killing the djinn responsible and getting the victims medical attention. In the case of Dean Winchester, by killing himself in the Fantasy Universe, he was able to awaken from the effects of the poison. By entering Charlie Bradbury's dreams and getting her to let go of the fear that was fueling the poison's effects, Dean was able to wake and cure her. After killing Neil, Dean stated that it was Neil's poison keeping a man in a coma and now that Neil was dead, the man would wake up.
At some point, the Campbell Family developed a djinn poison antidote that immediately reverses the effects of djinn poison on someone, ending their hallucinations if the djinn left them in a waking state instead of a coma. This antidote does not work on victims of "bastard off-shoot" djinn with Dean speculating that as the "bastard off-shoot" are a different kind of djinn, they need a different kind of antidote.
Hallucinations caused by supernatural means have some distinguished cures, like a psychological wall in the case of a hallucination caused by a trauma for being tortured in Hell. Hallucinations caused by the Ghost sickness will stop along with the sickness itself when the Buruburu responsible for it is put to rest. There's also the ones caused by War which stopped when his ring was taken from him.
In order to cure the Lance slowly poisoning an angel to death, the Lance must be broken as the Lance's power is in its craftsmanship and spellwork.
Killing the alpha of a Nachzehrer pack turns everyone that the pack alpha has changed back into humans.
Exposure to holy fire, even through being trapped in a circle of it, will cause the Rabid infection to burn away.
The British Men of Letters were able to create an experimental cure to lycanthropy using the live blood of the sire werewolf. It has only had one successful use. A previous attempt to cure a werewolf was unsuccessful and it was believed that no cure existed.
The antidote for the toxin contains taro root, a trace of arsenic and basidiomycota washed in holy water. The ingredients are then ground into a paste that is applied to the wound, neutralizing the toxin though it takes awhile for the subject to regain their strength.
Due to losing his grace, Jack's human and angel halves begin attacking each other, resulting in Jack becoming terminally ill with a total systemic organ failure. An attempt is made to cure him using some of Gabriel's grace and a spell from a shaman named Sergei, but the attempt fails and Jack dies. Lily Sunder comes up with a way to save Jack by using a ritual using Enochian magic to use the power of a piece of Jack's own soul to sustain him. The ritual's drawback is that it burns away the piece of Jack's soul in the process. Castiel resurrects Jack and he returns with his condition until he completes the ritual, curing Jack. However, this cure didn't appear to be permanent as Jack became ill again months later and again had to use the magic to heal himself.
After discovering that they are facing a gorgon, witch Rowena MacLeod came up with an antidote for gorgon venom. Most of the ingredients are unknown, but it requires regular antivenom. When used, only a small amount of the antidote was needed and could be applied through putting a few drops in the victim's mouth with an eyedropper. It did not work on angels however.
According to Sam, the antidote to thallium poisoning is something called Prussian Blue which the Winchesters have in the Men of Letters bunker. After Prophet Donatello Redfield is supposedly poisoned with thallium by Nick, Dean tries to give him the antidote only to learn that Nick injected Donatello with angel grace, not thallium and had lied.
This article is about a subject that is from official sources but is not considered canon.
Bobby Singer's Guide to Hunting states that the only way for a person who was bitten by a nagual to not become one is to consume the flesh of the nagual that bit that person (it's necessary to eat the whole nagual).
- Bobby Singer's Guide to Hunting (Nagual; non-canon)
- Supernatural: Coyote's Kiss (Borderwalker; non-canon)
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- While the Winchesters have only found ways to cure vampires, Rabids and werewolves, Sam Winchester suggests in Out of the Darkness, Into the Fire that there's a cure for anything if an attempt is made to find it. Indeed, subsequent to this, Sam found the cure for the Rabid infection and discovered the work the British Men of Letters had done on curing werewolves.