Medication, before a long time, goes to spoil (7)
I believe the answer is:
pillage
'to spoil' is the definition.
(thesaurus)
'medication before a long time' is the wordplay.
'medication' becomes 'pill' (pill is a kind of medication).
'before' is a charade indicator (letters next to each other).
'a long time' becomes 'age' (an age is a period of time).
'pill'+'age'='PILLAGE'
'goes' is the link.
(Other definitions for pillage that I've seen before include "Sacking" , "Violent stealing" , "Plunder, sack" , "Rob with violence" , "Loot" .)