Tea might be healthier so Sun argued uselessly (9)

I believe the answer is:

unsugared

'tea might be healthier so' is the definition.
(tea is healthier without sugar)

'sun argued uselessly' is the wordplay.
'uselessly' indicates anagramming the letters (a useless spelling).
'sun'+'argued'='sunargued'
'sunargued' anagrammed gives 'UNSUGARED'.

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app