Is it ok to smoke pot while on prednisone and on methotrexate?

Probably not.   The doctor should tell you though.   The Prednisone is a steriod, it has a ton of side effects, it is very hard on your body.    The Methotrexate is really powerful too, with brittle bones being its worst side effect.     There are others too, that is why you go so slow to your dosage, but I am not a doctor and can't remember the details.

I would not think you should be smoking anything, all you need is for your immune system to up and decide your lungs are problem and need to be destroyed.   This could happen.     Dermatomyositis is a serious auto-immune disease.    It can take lots of various forms, attack many organs.     I knew a boy a few years ago that had to attacking the brain.     It was horrible.

Tell your doctor everything you are taking.    They have heard it all before, they are not going to keel over in shock or anything.