Become disillusioned, I shed a few pounds outside hospital (4,5)
I believe the answer is:
lose faith
'become disillusioned i' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'shed a few pounds outside hospital' is the wordplay.
'shed' becomes 'lose' (I've seen this in another clue).
'a few pounds outside' becomes 'fait' (I can't explain this - if you can you should give a lot more credence to this answer).
'hospital' becomes 'H' (abbreviation for hospital).
'lose'+'fait'+'h'='LOSE FAITH'
Can you help me to learn more?
(Another definition for lose faith that I've seen is " See less reason to trust".)