Purgative wrapped inside polythene material (5)
I believe the answer is:
enema
'purgative' is the definition.
(thesaurus)
'wrapped inside polythene material' is the wordplay.
'wrapped inside' indicates a hidden word.
'ENEMA' is hidden in the letters of 'polythene material'.
(Other definitions for enema that I've seen before include "medicine to get you going" , "Procedure for vacating the bowels" , "Liquid injection given as a laxative" , "process to ensure evacuation" , "The bottom line in medical treatment?" .)