Heather comes over drunk with ecstasy - few people know about this (9)
I believe the answer is:
esoterica
'few people know about this' is the definition.
The definition suggests a singular noun which matches the answer.
'heather comes over drunk with ecstasy' is the wordplay.
'heather' becomes 'erica' (the plant genus Erica includes heather plants).
'comes over' means one lot of letters goes inside another.
'drunk' becomes 'sot' (both can mean someone who drinks too much).
'with' means one lot of letters go next to another.
'ecstasy' becomes 'E' (informal term for the drug).
'sot'+'e'='sote'
'erica' going around 'sote' is 'ESOTERICA'.
Can you help me to learn more?
(Other definitions for esoterica that I've seen before include "Specialized publications" , "narrow fields" , "Coarse tie? (anag)" , "collection of specialist stuff" , "Highly specialised subjects" .)