Patron saint of medicine originally involved in new cure (8)
I believe the answer is:
customer
'patron' is the definition.
(I've seen this before)
'saint of medicine originally involved in new cure' is the wordplay.
'saint' becomes 'st' (abbreviation).
'originally' suggests taking the first letters.
'involved in' indicates putting letters inside.
'new' indicates an anagram.
The initial letters of 'of medicine' is 'om'.
'st'+'om'='stom'
'cure' is an anagram of 'cuer'.
'stom' put inside 'cuer' is 'CUSTOMER'.
(Other definitions for customer that I've seen before include "Someone shopping" , "Rail passenger, nowadays" , "Patron" , "Person shopping" , "Shopper (or now rail passenger!)" .)