Expresses pain after having medicine that was intended to give comfort (6)
I believe the answer is:
pillow
'was intended to give comfort' is the definition.
I can't tell whether this defines the answer.
'expresses pain after having medicine' is the wordplay.
'expresses pain' becomes 'ow' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'after having' says to put letters next to each other.
'medicine' becomes 'pill' (pill is a kind of medicine).
'ow' put after 'pill' is 'PILLOW'.
'that' is the link.
Can you help me to learn more?
(Other definitions for pillow that I've seen before include "Item of bedding" , "Soft place for the head" , "place to lay his head" , "Head supporter in bed" , "Bolster, perhaps" .)