Charlie stops negotiating drugs course (10)
I believe the answer is:
medication
'drugs course' is the definition.
(a course of drugs)
'charlie stops negotiating' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'stops' indicates putting letters inside.
'negotiating' becomes 'mediation' (negotiation between multiple parties).
'c' inserted within 'mediation' is 'MEDICATION'.
(Other definitions for medication that I've seen before include "drugs etc." , "treatment regime" .)