Unknown fate when swallowing drug with a fanatic (6)
I believe the answer is:
zealot
'fanatic' is the definition.
(I've seen this before)
'unknown fate when swallowing drug with a' is the wordplay.
'unknown' becomes 'z' (algebra).
'fate' becomes 'lot' (synonyms).
'when swallowing' is an insertion indicator.
'drug' becomes 'e' (e is another name for ecstasy).
'with' indicates putting letters inside.
'z'+'lot'='zlot'
'zlot' placed around 'e' is 'zelot'.
'zelot' going around 'a' is 'ZEALOT'.
(Other definitions for zealot that I've seen before include "A fanatic or over-enthusiastic person" , "Fanatical believer" , "Fanatic for a cause" , "Single-minded supporter of a cause" , "A fanatic or extremist" .)