Calming drug (8)
I believe the answer is:
sedative
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">calming drug</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 sedative that I've seen before include "quieter" , "Drug to make one sleep" , "having soothing effect" , "Sleeping drug" , "Tranquillising drug" .)