Take in doctor with writing material (5)
I believe the answer is:
drink
'take in' is the definition.
(I know that drink is a more specific form of take in)
'doctor with writing material' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'with' means one lot of letters go next to another.
'writing material' becomes 'ink' (substance for writing with).
'dr'+'ink'='DRINK'
(Other definitions for drink that I've seen before include "Possibly shake" , "vodka, perhaps?" , "effect rehydration" , "Swallow" , "Booze" .)