Medicine can start to taste awful, stopping relief (7)
I believe the answer is:
antacid
'medicine' is the definition.
(I've seen this before)
'can start to taste awful stopping relief' is the wordplay.
'start to' says to take the initial letters.
'awful' is an anagram indicator.
'stopping' indicates putting letters inside (inserted letters stop or plug a gap).
'relief' becomes 'aid' (I've seen this in other clues).
The first letter of 'taste' is 't'.
'can'+'t'='cant'
'cant' anagrammed gives 'ntac'.
'ntac' inserted inside 'aid' is 'ANTACID'.
(Other definitions for antacid that I've seen before include "calming agent" , "remedy for tummy trouble?" , "Stomach drug" , "Medicine to settle the stomach" , "Substance used to treat stomach upsert" .)