Substance injected into the body of a Wraith victim during the feeding process. The process is so traumatic for the individual that, without it, he or she would die far faster than the Wraith wish. This enzyme is injected gradually and ensures that the heart will continue to beat, permitting a Wraith to take more time killing the person.
An overdose of this enzyme can give a person super-human strength, paranoia, and a loss of rational thought -- should he survive the ordeal.
The Siege, Part 3 - A Wraith begins to feed on Lieutenant Ford but a grenade kills the creature, injecting Aiden flooding his system with the enzyme. When he wakes up he becomes paranoid and flees Atlantis.
Runner - Several members of the Atlantis expedition team manage to find Ford and discover he is still killing Wraith, harvesting their enzyme -- to which he has become addicted.
The Hive - Dr. McKay takes a massive dose of the enzyme to defeat his captors and return to Atlantis, where he is restrained as his high dissipates. Meanwhile, an absence of the enzyme in their hive ship cells kills Kanayo and nearly destroys Ford as well.