The Cure was introduced during Season 4 of The Vampire Diaries becoming a key point in the story and four vampires used this cure to regain their humanity!
In the 1st century BC, in The Vampire Diaries, the ancestor of Bonnie Bennett, Qetsiyah fell in love with another wizard named Silas. She was the one who created a spell to make them immortal but after Silas’ betrayal, she also created a cure (The Cure) to undo her spell. Instead of taking it, Silas chose to remain entombed in a cave on a remote island for 2,000 years. During Season 4 of The Vampire Diaries, Atticus Shane convinced Elena and her friends to help him raise Silas from the dead in exchange for The Cure. It was only after they arrived on the island that they learned that there was only one dose. The Cure changed hands throughout the second half of the season. Eventually, four vampires were able to take or taste this remedy to regain their humanity in The Vampire Diaries!
Once Elena had the cure, she offered it to Stefan. However, he didn’t take it and he set up the big twist in the season 4 finale of The Vampire Diaries. During a brutal confrontation with Katherine, Elena was forced to shove the cure down her doppelgänger’s throat to save herself.
After spending most of Season 6 in the prison world of 1994, Bonnie returned to present-day Mystic Falls with the cure. Damon gave it to Elena and offered to take it as well. Once Elena drank the cure, Damon planned to feed off of her, and as long as no one sucked it, he and Elena could live out the rest of their lives together as mortals.. Despite Elena and Damon’s uncertainties about their future, she took the cure. All the memories of Damon that Alaric had forced Elena to forget came flooding back. But Damon didn’t have time to finish his plan and Kai linked Elena’s life to Bonnie’s…
The last season of The Vampire Diaries was the darkest… Bonnie used a syringe to draw Elena’s blood to use on Cade, but eventually her plan changed. When a humanless Stefan arrived at Bonnie’s house intent on killing Elena, the witch injected him with the cure., making him the first vampire to successfully transition into a human without directly drinking the cure. Stefan relived every murder he committed, and everyone he forced began to remember the things Stefan wanted them to forget.
Much to the surprise, Damon was the last vampire to take the cure to become human again.. During the Series Finale of The Vampire Diaries, the two Salvatore brothers were willing to sacrifice themselves to save Mystic Falls, but Stefan injected his older brother’s blood and took Damon’s place. Stefan’s death ensured the destruction of Katherine and Hell, and it was a pivotal moment in Stefan’s quest for redemption. This is how Damon became human again and was able to live happy and peaceful days with Elena. Julie Plec hinted that eventually Rebekah was the last vampire to use it.