The Cure, also known as the Cure for Immortality or the Cure for Vampirism, is one of the three known ways to reverse immortality, or more colloquially, vampirism.
"The Cure" is a potion created by the witch Qetsiyah to reverse immortality. When used on immortal beings, they are reverted to their mortal states and are thus vulnerable to death. The Immortality Reversal Spell or "second cure" was a spell created by Esther for her children to undo the curse she originally gave them. The final "cure" is another spell invented by the Travelers using the blood from the last pair of doppelgängers and a minor version of the Magic Purification Spell. Should a vampire drink the mixed doppelgänger blood coupled with the spell, it will undo all of the magic that turned the person into a vampire. The spell will, however, return the individual to the last state they were in prior to becoming a vampire, their death.
When the cure is ingested, the blood of the individual is converted; a "living" version of the cure. They become a viable candidate for a single dose. Should it be removed, whether in partial or full, and the individual in question had lived beyond their human years, the post-cure effects would begin to cause them to age and eventually die such as what happened with Katherine Pierce.
During the creation of two alternate dimensions by the Gemini Coven in 1903 and 1994, the effects of these dimentions duplicated all magical items, objects, and talismans therein; the ripple effect also created alternate versions of the cure. The 1994 version of the cure was discovered by Bonnie Bennett while searching for Silas' Tombstone on Nova Scotia in the 1994 prison world and she took it back to Earth. The non-duplicated version of the Cure perished along with Amara whereas 1994 cure is held by Damon.