Drugs ring spreads to cover island (7)
I believe the answer is:
opiates
'drugs' is the definition.
(opiate is a kind of drug)
'ring spreads to cover island' is the wordplay.
'ring' becomes 'o'.
'spreads' becomes 'pates' (pate is a kind of spread**).
'to cover' is an insertion indicator.
'island' becomes 'i'.
'pates' placed around 'i' is 'piates'.
'o'+'piates'='OPIATES'
(Other definitions for opiates that I've seen before include "Makes dull" , "Branch of narcotics" , "Drugs that dull the feelings, sedatives" , "Is a poet (anag.)" , "Sedative drugs" .)