Realizing that Dean was likely next on the djinn's list, Sam followed Dean and found him near death from hallucinations of the Prince of Hell Azazel. Just before Dean could die, Sam injected him directly in the heart with the antidote, saving Dean's life. After Sam and Samuel explained what had happened, Dean was shocked to learn that Samuel had a cure for djinn poison. Samuel told Dean that he knew things that "your daddy never even dreamed" of such as the antidote.
The next night, while waiting for the djinn to strike, Dean spotted Brigitta and one of her brothers attacking Sid and his wife. Armed with two syringes of the antidote, Dean rushed to their rescue, only to discover Sid and his wife already dead. Dean was then ambushed by the two djinn who destroyed the syringes of antidote and infected Dean with a "double dose" of their poison. After Sam and Samuel killed Brigitta's brothers, Sam rushed to Dean's aid in time with the antidote while Samuel and Christian dealt with Brigitta.
After Charlie Bradbury was poisoned by the "bastard off-shoot" djinn Jennifer O'Brien, Sam injected her with the antidote to no effect. Dean theorized that as it was a different sort of djinn, they needed a different sort of antidote. Instead, Dean used African Dream Root to enter Charlie's dreams and save her from the inside.
The ingredients for the antidote are unknown but it takes the form a liquid that a syringe is filled with. The substance is injected directly into the djinn victim, instantly curing them of the djinn poison. When Dean Winchester was injected, his brother injected him directly in the heart. However, when Sam injected Charlie Bradbury, he merely injected her in the arm.
The antidote does not work on the poison of the "bastard off-shoot" of djinn. The Winchesters speculated that as its a different type of djinn, it needs a different type of antidote.