Vitura is a drug that makes its users highly susceptible to suggestion. It also causes memory loss.
Vitura was used on Thea Queen by Malcolm Merlyn in order to have her kill Sara. Malcolm then blackmailed Oliver to have to face the League of Assassins on her behalf and, were he to kill Ra's al Ghul, he would thereby clear Malcolm's blood debt.
Arrow: Season 2.5
- "Awakenings" (mentioned)