Procedure used for drug overdose (6)
I believe the answer is:
method
'procedure' is the definition.
(I've seen this before)
'drug overdose' is the wordplay.
'drug' becomes 'meth' (meth is a kind of drug).
'overdose' becomes 'o.d.' (synonyms).
'meth'+'od'='METHOD'
'used for' acts as a link.
(Other definitions for method that I've seen before include "Way of doing something, even in madness (6)" , "Fashion" , "System (of acting?)" , "Order" , "Process, esp. Stanislavsky's" .)