Made heavy demands on (5)
I believe the answer is:
taxed
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">made heavy demands on</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 taxed that I've seen before include "Was demanding" , "Levied a duty on" , "Made heavy demands on" , "Heavily burdened" , "Imposed duty on" .)