Congress is told what it can and cannot do in Article 1 of the Constitution. Federal Government does not have power over everything. If there is something new and the power to that has not been assigned to Congress then it goes to the States Government.
Even though people may not want to hear or prefer not to listen the law is pretty straight forward. When the Federal and State laws collide the Federal law will most likely always win. Example States law says that marijuana has a medical purpose and should be legalized for that purpose only. Federal law does not agree with this and it is denied. Federal law wins.
The Michigan Medical Marijuana Act states that a person has the right to use and grow if it is medically proven that they need it. There can be growers and it can be sold in specialty stores to people with a prescription. This is against a Federal law and makes all these acts illegal. Economically the sale of medical marijuana could help Michigan out. Like the sales of cigarettes and alcohol this too could be taxed. Farmers could benefit as well.
The Federal Government could argue that it is indeed an illegal drug and should be kept that way. That even though its purpose is for medical use only, how many other people would have access to it. It has not been approved by the FDA as a safe and affective medical drug. And because they said so and they have the power to deny it and they will.
The Federal and State Governments should be working together on this issue not fighting, for the people that actually benefit from the use of this and are hiding the fact that they are using it so they