The doctor will tell you avoiding stress has a cheering effect (4,4,5,4)
I believe the answer is:
does ones heart good
'the' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.
'doctor will tell you avoiding stress has a cheering effect' is the wordplay.
I cannot really understand how this works, but
'doctor' could be 'ear' (ear doctor is a kind of doctor) and 'ear' is found within the answer.
'you' could be 'one' (I've seen this before) and 'one' is found within the answer.
'effect' could be 'do' ('do' can be a synonym of 'effect') and 'do' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?