Sentence:  No sooner has a [synthetic] drug been blacklisted than chemists adjust their recipe and start churning out a subtly different one. These "legal highs" are sold for the few months it takes the authorities to identify and <WSD>ban</WSD> them, and then the cycle begins again. 
Meaning of the word marked with <WSD> tags:  To prohibit; to interdict; to proscribe; to forbid or block from participation.