Procedure involving drug’s expensive (5)
I believe the answer is:
steep
'expensive' is the definition.
(I've seen this before)
'procedure involving drug's' is the wordplay.
'procedure' becomes 'step' (I am not sure about this - if you are sure you should believe this answer much more).
'involving' is an insertion indicator.
'drug' becomes 'e' (e is another name for ecstasy).
'step' placed around 'e' is 'STEEP'.
Can you help me to learn more?
(Other definitions for steep that I've seen before include "Rapidly rising" , "Marinate" , "Saturate; precipitous" , "Almost perpendicular" , "not reasonable" .)