I mismanage folk developing laxative (4,2,8)
I believe the answer is:
milk of magnesia
'laxative' is the definition.
(milk of magnesia is a kind of laxative)
'i mismanage folk developing' is the wordplay.
'developing' indicates anagramming the letters (letters developed into a new form).
'i'+'mismanage'+'folk'='imismanagefolk'
'imismanagefolk' is an anagram of 'MILK OF MAGNESIA'.
(Other definitions for milk of magnesia that I've seen before include "laxative" , "Antacid preparation" .)