Freed soldier survived swallowing drug (8)
I believe the answer is:
relieved
'freed' is the definition.
('relieve' can be a synonym of 'free')
'soldier survived swallowing drug' is the wordplay.
'soldier' becomes 'RE' (Royal Engineer).
'survived' becomes 'lived' ('live' can be a synonym of 'survive').
'swallowing' indicates putting letters inside.
'drug' becomes 'e' (E is another name for ecstasy).
'lived' enclosing 'e' is 'lieved'.
're'+'lieved'='RELIEVED'
(Other definitions for relieved that I've seen before include "Liberated" , "Freed from anxiety or duty" , "No longer distressed, reassured" , "Thankful" , "Freed from distress" .)