Food preserver, say, like a drug (not cocaine) (8)
I believe the answer is:
additive
'food preserver say' is the definition.
(preservatives are a type of food additive)
'like a drug not cocaine' is the wordplay.
'like a drug' becomes 'addictive' (drugs are addictive).
'not' is a deletion indicator.
'cocaine' becomes 'C' (drugs abbreviation).
'addictive' with 'c' taken away is 'ADDITIVE'.
(Other definitions for additive that I've seen before include "Something extra in food" , "Eg, a colorant or preservative in foods" , "Something joined, to food say" , "Such as a colorant or preservative in foodstuffs" , "Tie David up with added substance" .)