Ruins case of synthetic drugs (8)
I believe the answer is:
scuppers
'ruins' is the definition.
(I've seen this before)
'case of synthetic drugs' is the wordplay.
'case of' says to hollow out the word (remove centre letters) (outsides of).
'drugs' becomes 'uppers' (upper is a kind of drug).
'synthetic' with its centre taken out is 'sc'.
'sc'+'uppers'='SCUPPERS'
(Other definitions for scuppers that I've seen before include "Ruins" , "Ship's drainage holes" , "drains aboard" , "Drain holes in ship" , "Openings in ship's sides to carry off water from deck" .)