Smoker invested in inhalant expecting returns (4)
I believe the answer is:
etna
'smoker' is the definition.
(volcano Mount Etna, something which 'smokes')
'invested in inhalant expecting returns' is the wordplay.
'invested in' indicates the answer is hidden within the clue.
'returns' is a reversal indicator.
'ante' is hidden within 'inhalant expecting'.
'ante' in reverse letter order is 'ETNA'.
(Other definitions for etna that I've seen before include "Dangerous peak" , "Italian volcano" , "Italian smoker" , "Heating vessel" , "Volcano in Sicily, quite neat" .)