Say no, it doesn't make you feel sick? (8)
I believe the answer is:
disagree
'say no' is the definition.
(thesaurus)
'it doesn't make you feel sick?' is the wordplay.
I cannot quite see how this works, but
'it' could be 'sa' (SA can mean sex appeal, as in 'it') and 'sa' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for disagree that I've seen before include "Beg to differ" , "Take a different view" , "Differ, take issue" , "Have a conflicting opinion" , "Differ, object" .)