Sailor takes heroin, sees wild goat (4)
I believe the answer is:
tahr
'wild goat' is the definition.
(I've seen this in another clue)
'sailor takes heroin' is the wordplay.
'sailor' becomes 'tar' (slang term for a sailor).
'takes' is an insertion indicator.
'heroin' becomes 'H' (H is a slang term for heroin).
'tar' enclosing 'h' is 'TAHR'.
'sees' acts as a link.
(Other definitions for tahr that I've seen before include "animal" , "goat in Himalayas" , "Himalayan goat" , "Muslim ruler; ere me (anag.)" .)