Doctor gets girls thick syrup (8)
I believe the answer is:
molasses
'thick syrup' is the definition.
(I've seen this in another clue)
'doctor gets girls' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'gets' means one lot of letters go next to another.
'girls' becomes 'lasses' (lass can mean a girl).
'mo'+'lasses'='MOLASSES'
(Other definitions for molasses that I've seen before include "Thick dark syrup made from sugar cane" , "Black treacle" , "Syrupy stuff" , "Slow runner" , "sticky food" .)