Harry brought back jam Mike's left in pot (5)
I believe the answer is:
ganja
'pot' is the definition.
(synonyms)
'harry brought back jam mike's left' is the wordplay.
'harry' becomes 'nag' (both can mean to consistently bother).
'brought back' is a reversal indicator.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'left' is a deletion indicator (some letters have left).
'nag' in reverse letter order is 'gan'.
'jam' with 'm' removed is 'ja'.
'gan'+'ja'='GANJA'
'in' is the link.
(Other definitions for ganja that I've seen before include "Marijuana" , "Strong pot" , "Potent type of cannabis" , "blow" , "Strong cannabis" .)