Deal with a druggie (5)
I believe the answer is:
doper
'druggie' is the definition.
I can't judge whether this definition defines the answer.
'deal with a' is the wordplay.
'deal with' becomes 'do'.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'do'+'per'='DOPER'
Can you help me to learn more?
(Other definitions for doper that I've seen before include "One administering an illegal drug" , "One who administers illegal substances to animals" , "drugs cheat" .)