Drug brought about everything in break-up of one band (10)
I believe the answer is:
belladonna
'drug' is the definition.
(thesaurus)
'brought about everything in break-up of one band' is the wordplay.
'brought about' says the letters should be written in reverse.
'everything' becomes 'all' (I've seen this before).
'in' indicates putting letters inside.
'break up of' indicates anagramming the letters (I've seen 'break up' mean this).
'all' in reverse letter order is 'lla'.
'one'+'band'='oneband'
'oneband' is an anagram of 'bedonna'.
'lla' placed inside 'bedonna' is 'BELLADONNA'.
(Other definitions for belladonna that I've seen before include "Drug made from deadly nightshade" , "drug supplier" , "Could it poison" , "Deadly nightshade or atropine" , "brought a sparkle to the eye" .)