Ethical drug gives confidence (6)
I believe the answer is:
morale
'confidence' is the definition.
(thesaurus)
'ethical drug' is the wordplay.
'ethical' becomes 'moral' ('moral' can be a synonym of 'ethical').
'drug' becomes 'e' (e is another name for ecstasy).
'moral'+'e'='MORALE'
'gives' acts as a link.
(Other definitions for morale that I've seen before include "Feeling of well-being" , "Strength of purpose" , "State of a group's confidence and spirit" , "Degree of optimism (of troops, perhaps)" , "Team spirit" .)