Taking drug, get better for unrehearsed performance (6)
I believe the answer is:
improv
'unrehearsed performance' is the definition.
(improvisation)
'taking drug get better' is the wordplay.
'taking' is a deletion indicator.
'drug' becomes 'e' (E is another name for ecstasy).
'get better' becomes 'improve' (I've seen this before).
'improve' with 'e' taken away is 'IMPROV'.
'for' is the link.
(Other definitions for improv that I've seen before include "off-the-cuff humour" , "Off-the-cuff comedy" , "little ad-libbing" , "Stand-up comedy, perhaps" .)