LSD, say (12)
I believe the answer is:
hallucinogen
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">lsd say</span>' is the definition.<br/ ><span class="explanation-format__explanation">(lsd is a kind of hallucinogen)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for hallucinogen that I've seen before include "Mind-altering drug" , "mind-blowing" , "Mind-affecting drug" , "Drug inducing unreal perceptions" , "Drug such as LSD" .)