First to do drug trials can't stand (7)
I believe the answer is:
detests
'can't stand' is the definition.
(I've seen this in another clue)
'first to do drug trials' is the wordplay.
'first to' indicates taking the first letters.
'drug' becomes 'e' (E is another name for ecstasy).
'trials' becomes 'tests' ('test' can be a synonym of 'trial').
The first letter of 'do' is 'd'.
'd'+'e'+'tests'='DETESTS'
(Other definitions for detests that I've seen before include "Abominates" , "Loathes" , "Hates" , "Abhors" , "Cordially loathe" .)