Trouble coming after ring names a drug supplier (10)
I believe the answer is:
belladonna
'drug supplier' is the definition.
(I've seen this before)
'trouble coming after ring names a' is the wordplay.
'trouble' becomes 'ado' (both can mean bother or commotion).
'coming after' is a charade indicator (letters next to each other).
'ring' becomes 'bell' (both can mean to call on the phone).
'names' becomes 'nn' (an abbreviation for name twice).
'ado' put after 'bell' is 'bellado'.
'bellado'+'nn'+'a'='BELLADONNA'
(Other definitions for belladonna that I've seen before include "drug supplier" , "Deadly nightshade or atropine" , "brought a sparkle to the eye" , "Could it poison" , "Drug made from deadly nightshade" .)