Sentence:  As the world's drug habit shows, governments are failing in their quest to monitor every London window-box and Andean hillside for banned plants. But even that Sisyphean task looks easy next to the fight against synthetic drugs. No sooner has a drug been blacklisted than chemists adjust their <WSD>recipe</WSD> and start churning out a subtly different one. 
Meaning of the word marked with <WSD> tags:  A formula for preparing or using a medicine; a prescription; also, a medicine prepared from such instructions. (from 16th c.)