well unless you live in one of the states that permits the use of medical marijuana (and you have a valid prescription for it) then the law says you shouldn't be using it at all. but let's assume you do have a medical marijuana prescription. in general i wouldn't think smoking cannabis would interfere with the action of prednisone. prednisone is a steroid preparation that treats inflammatory conditions. i must add however that few studies have been done to evaluate potential drug interactions with marijuana. so the real answer to your question is: we just don't know if using marijuana while taking prednisone is harmful or not. hope that helps!
is it harmful to use cannabis while taking prednisone?