I do take methyl prednissolone (8mg equal to 10 mg pred). My rheumy does not think that MTX works for PMR- and my genetics says it wouldn't work for me anyway. I have a certain kind of pain in my arm muscles that happen with PMR when it is active that I haven't had for a while. I have so much going on with my body that is not PMR that I don't want to bore you with but I feel that I have the PMR on the run. I have put my taper "on hold" right now because of other health challenges. I'm pretty sure that MSM doesn't interact with other meds but a check with drugs.com might be good.