Doctor on crack and dope (6)
I believe the answer is:
drongo
'dope' is the definition.
(I've seen this before)
'doctor on crack' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'crack' becomes 'go' (to have a crack is to have a go or turn).
'dr'+'on'+'go'='DRONGO'
'and' is the link.
(Other definitions for drongo that I've seen before include "dope" , "Long-tailed songbird" , "Australian fool - Gordon (anag)" , "Bird - Aussie fool - Gordon (anag)" , "Bird -- idiot (in Australia)" .)