Because cannabis is illegal on the federal level, it is federally illegal for registered cannabis patients to own a firearm in any state. But some states are pushing back against this and either suing to protect MMJ patients' 2nd Amendment rights, or are passing laws to protect patients on a state level. Michigan is not one of these states yet, but we'll update when they are. Meanwhile, you should talk to a competent attorney if you have questions about gun ownership and cannabis.