They are thorny problems, regularly treated with balm (8)
I believe the answer is:
brambles
'they are thorny' is the definition.
The definition suggests an adverb but the answer is not.
'problems regularly treated with balm' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'treated with' indicates anagramming the letters.
The alternating letters of 'problems' are 'rbes'.
'rbes' with its letters anagrammed with 'balm' gives 'BRAMBLES'.
Can you help me to learn more?
(Other definitions for brambles that I've seen before include "Prickly shrubs" , "Rough thorny shrubs or vines" , "Various rough thorny shrubs" .)