Substance derived from ground-up Goa'uld symbiotes, responsible for maintaining the perfect health of the host body -- functioning as an alternate (and superior) immune system, like having a symbiote (but without the symbiote). The drug is administered with a tretonin injector.
The drug was created by the Pangarans, who got 20 percent of their population dependent on the substance before realizing that it caused the user's immune system to cease to function.
Cure - The Pangarans introduce tretonin to SG-1, and confess that they cannot live without it. The Tok'ra queen, Egeria, saves their lives by reversing their dependence on tretonin before she dies.
The Changeling - Teal'c and Bra'tac lose their symbiotes, and are forced to rely on tretonin to sustain their lives.
Birthright - SG-1 tries to convince the Hak'tyl, a proud tribe of female Jaffa, to take tretonin, and find after drug trials that converting from a larval symbiote has a high mortality rate.
Sacrifices - Teal'c receives an air-drop of tretonin from a U.A.V., and rushes to deliver a dose to Ishta -- who is being tortured by Moloc.
Stronghold - Baal baits Teal'c with his only supply of tretonin to bring him to accept the former System Lord's offer.
Dominion - Thanks to tretonin and his lack of a symbiote, a Jaffa survives Baal's deployment of symbiote poison to kill off his clones.