This drug doesn't work, man (4)
I believe the answer is:
dude
'man' is the definition.
(I know that dude is a type of man)
'this drug doesn't work' is the wordplay.
I cannot really see how this works, but
'drug' could be 'e' (E is another name for ecstasy) and 'e' is located in the answer.
The remaining letters 'dud' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for dude that I've seen before include "Man (US colloq.)" , "Dandy - US or Canadian city dweller" , "Fellow" , "Dandy - city dweller holidaying on ranch" , "He's no cowboy" .)