Crazy combination of drugs (8)
I believe the answer is:
crackpot
'crazy' is the definition.
(I've seen this before)
'combination of drugs' is the wordplay.
'combination of' becomes 'crack' (I am not sure about this - if you are sure you should believe this answer much more).
'drugs' becomes 'pot' (slang term for mariujana).
'crack'+'pot'='CRACKPOT'
Can you help me to learn more?
(Other definitions for crackpot that I've seen before include "Eccentric (colloq.)" , "Bats" , "Damage utensil for informally eccentric person" , "Fruitcake, screwball" , "Odd" .)