Michigan recognizes medical marijuana patients from other states, and has dispensaries. Yet the dispensaries are not licensed at the state level, and some will sell to out of state patients but others will not.
Possession of marijuana is illegal in Michigan unless you have a debilitating medical condition i.e. medical card. If you are arrested for possession of marijuana in Michigan, and do not have a debilitating medical condition or medical card, the penalties you face will depend on your intent in possessing the marijuana.
Marijuana use in Michigan is illegal without a valid medical condition, and is a $100 charge, misdemeanor and a 90 day max jail sentence. Medical marijuana patients either have to grow it themselves, or obtain it from a caregiver, who may not dispense it to no more than five patients. As it varies from county to county, the purchase of medicinal marijuana in Michigan with be extremely difficult to do, legally. Searching for dispensaries online, may be your best bet.
If you are looking to buy medical marijuana in Michigan then you need to first make sure that you have a medical marijuana card. Once you have gone to the doctor and got that then you can go to a dispensary in Michigan and show all the proper documentation so that you can purchase your medical marijuana.