Roshna is a liquid compound to which the Goa'uld have made Aris Boch's race, the Ilempiri addicted to. Since the Goa'uld are genetically incapable of taking on this species as hosts, they devised another way to keep themselves in power. Without roshna, Boch's species would die.
Roshna can be administered in the appearance of an additional flavoring for a drink, or taken directly into the mouth. Aris Boch is hopeful that an antidote to the drug will be discovered, and gave Major Samantha Carter a sample for her to study in the hopes that one day his people may be freed from their subservience. (SG1: "Deadman Switch")