Jam one drug inside another (5)
I believe the answer is:
choke
'jam' is the definition.
(choking is a kind of jamming)
'one drug inside another' is the wordplay.
'one drug' becomes 'C' (C is an example).
'inside another' becomes 'hoke' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'c'+'hoke'='CHOKE'
(Other definitions for choke that I've seen before include "Asphyxiate" , "Constrict the throat" , "Become speechless (with emotion)" , "Throttle" , "Strangle" .)