Doctor - it's a pleasure (5)
I believe the answer is:
treat
'doctor' is the definition.
(doctor can mean to give medical treatment)
'it's a pleasure' is the wordplay.
I cannot quite see how this works, but
'a' is within the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
The remaining letters 'ret' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for treat that I've seen before include "Give care to; surprise gift" , "Unexpected surprise" , "Pay for - minister to - deal with" , "Handle - pleasure given" , "Deal with - source of great pleasure" .)