Doctor devoured treat (8)
I believe the answer is:
medicate
'treat' is the definition.
(I know that medicate is a more specific form of the action the treat)
'doctor devoured' is the wordplay.
'doctor' becomes 'medic' (doctor is a type of medic).
'devoured' becomes 'ate' (to devour is to eat).
'medic'+'ate'='MEDICATE'
(Other definitions for medicate that I've seen before include "Give a drug to" , "Supply drugs" , "Treat (one) with drugs" , "Treat with pills, drugs etc" , "Administer a drug to" .)