Codeine source (5)
I believe the answer is:
opium
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">codeine source</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for opium that I've seen before include "wars with China" , "Poppy-based drug" , "where horse originally came from?" , "Poppy drug" , "Dried juice of white poppy" .)