Gas? I mean to change laxative (8)
I believe the answer is:
magnesia
'laxative' is the definition.
(I've seen this before)
'gas? i mean to change' is the wordplay.
'to change' indicates an anagram.
'gas'+'i'+'mean'='gasimean'
'gasimean' anagrammed gives 'MAGNESIA'.
(Other definitions for magnesia that I've seen before include "Asian gem (anag) - milk of ___" , "laxative" , "Carbonate used as an antacid" , "Is Ma easing off the white mineral?" , "Medicinal powder" .)