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.
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.
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.
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.