Demanding to take dope during leave (7)
I believe the answer is:
exigent
'demanding' is the definition.
(similar in meaning)
'dope during leave' is the wordplay.
'dope' becomes 'gen' (I've seen this in other clues).
'during' indicates putting letters inside.
'leave' becomes 'exit' (synonyms).
'gen' going within 'exit' is 'EXIGENT'.
'to take' acts as a link.
(Other definitions for exigent that I've seen before include "Pressing; demanding" , "Demanding immediate attention" , "Pressing and urgent" , "Urgent and exacting" , "Exacting, requiring much" .)