Horse, ecstasy and smack are on the rise (4)
I believe the answer is:
mare
'horse' is the definition.
(mare is a kind of horse)
'ecstasy and smack are on the rise' is the wordplay.
'ecstasy' becomes 'e' (informal term for the drug).
'and' is a charade indicator (letters next to each other).
'smack are' becomes 'ram' (I can't explain this - if you can you should believe this answer much more).
'on the rise' is a reversal indicator.
'e'+'ram'='eram'
'eram' back-to-front is 'MARE'.
Can you help me to learn more?
(Other definitions for mare that I've seen before include "Female quadruped" , "A night-time strangler" , "Female equine animal" , "Ream (anag)" , "For classicists, sea" .)