By law, liquor regularly taken with drug (4)
I believe the answer is:
iure
'by law' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'liquor regularly taken with drug' is the wordplay.
'regularly taken' indicates alternate letters (letters removed at regular intervals).
'with' is a charade indicator (letters next to each other).
'drug' becomes 'e' (E is another name for ecstasy).
The alternate letters of 'liquor' are 'iur'.
'iur'+'e'='IURE'
Can you help me to learn more?
(Other definitions for iure that I've seen before include "by law by Cicero" , "by right" .)