Antacid (6)
I believe the answer is:
bicarb
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">antacid</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for bicarb that I've seen before include "What helps raise" , "source of fizz?" , "baking aid" , "Raising agent in baking (colloq.)" , "It helps digestion" .)