From The Stargate Omnipedia
A liquid compound to which the Goa'uld have made Aris Boch's race addicted. Since the Goa'uld are genetically incapable of taking on this species as hosts, they devised another way to keep themselves in power. Without roshnah, Aris Boch's species die.
Roshnah can be administered in the appearance of an additional flavoring for a drink, or taken directly into the mouth.
Deadman Switch - Boch gives Carter a sample of roshnah in hopes that she may, one day, discover an antidote which will prevent his people from depending on it for their survival.