Close to collapse, mate swallows one herbal remedy (9)
I believe the answer is:
echinacea
'herbal remedy' is the definition.
(I've seen this before)
'close to collapse mate swallows one' is the wordplay.
'close to' says to take the final letters (the close of something is the end).
'mate' becomes 'china' (cockney rhyming slang, mate is china plate).
'swallows one' becomes 'cea' (I can't justify this - if you can you should give a lot more credence to this answer).
The last letter of 'collapse' is 'e'.
'e'+'china'+'cea'='ECHINACEA'
Can you help me to learn more?
(Other definitions for echinacea that I've seen before include "Herb" , "Plant of the daisy family used as a herbal remedy" .)