Brainwash - do it in trance perhaps (12)
I believe the answer is:
indoctrinate
'brainwash' is the definition.
(thesaurus)
'do it in trance perhaps' is the wordplay.
'perhaps' indicates anagramming the letters.
'do'+'it'+'in'+'trance'='doitintrance'
'doitintrance' with letters rearranged gives 'INDOCTRINATE'.
(Other definitions for indoctrinate that I've seen before include "attempt to brainwash" , "change ideology" , "Imbue (someone) with an opinion" .)