Roshna is the drug Aris Boch and others of his kind became addicted to under the Goa'uld.
After SG-1 were captured by the bounty hunter Aris Boch, they noticed he would mix a blue liquid into his canteen before drinking it. He was very circumpect about this "flavoring", but the Tok'ra spy Korra later revealed the Goa'uld put roshna into Boch's people's drinking supply for generations. The Goa'uld could not use them for hosts, and thus used roshna to keep Boch's people enslaved to them. The people were addicted to the alien additive, which seemed to be something that the Goa'uld alone could provide. Without roshna, Aris Boch would die.
After Boch had a change of heart and freed the team and Korra, he gave a sample of roshna to Samantha Carter. She had offered to help find a way to prevent his people's dependence on the drug, and he hoped she could live up to her promise.
--Aurora 15:30, 21 November 2008 (PST)