I dont know first hand but it sounds like Newt does. The weed has been prooven time and again for serious illness. It beats getting hooked on the heavy drugs / pain killers too!

Mal: "Y'all see the man hanging out of the spaceship with the really big gun?{ref, Jayne} Man's lookin' to kill some folk. So really, it's his will y'all should worry about thwarting."