A doctor with it has one on drive (8)
I believe the answer is:
ambition
'drive' is the definition.
(I know that ambition is a type of drive)
'a doctor with it has one on' is the wordplay.
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus).
'with' is a charade indicator (letters next to each other).
'has' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'a'+'mb'+'it'+'i'+'on'='AMBITION'
(Other definitions for ambition that I've seen before include "Target" , "Objective" , "Desire to get on" , "Desire for success or power" , "wanting to succeed" .)