Tranquillised (7)
I believe the answer is:
sedated
'tranquillised' is the definition.
('sedate' can be a synonym of 'tranquillize')
This is all the clue.
(Other definitions for sedated that I've seen before include "Calmed with drugs" , "Dead set (anag) - tranquillised" , "Under the influence of drugs" , "Given calming drugs" , "kept calm" .)