Snort ice, a synthetic drug (9)
I believe the answer is:
narcotise
'drug' is the definition.
('drug'->'narcotize' is in my internal thesaurus and 'ize'->'ise')
'snort ice a synthetic' is the wordplay.
'synthetic' is an anagram indicator.
'snort'+'ice'+'a'='snorticea'
'snorticea' with letters rearranged gives 'NARCOTISE'.
(Other definitions for narcotise that I've seen before include "Numb" , "administer drug" , "put under influence of drugs" .)