It's hard to swallow with a brittle lip problem (6,4)
I believe the answer is:
bitter pill
'it's hard to swallow' is the definition.
(I've seen this in another clue)
'with a brittle lip problem' is the wordplay.
'with' says to put letters next to each other.
'problem' indicates an anagram.
'brittle' put next to 'lip' is 'brittlelip'.
'brittlelip' anagrammed gives 'BITTER PILL'.
(Other definitions for bitter pill that I've seen before include "It's hard to take" , "One unpleasant to swallow" .)