LANSING, MI (WTVB) - Michigan medical marijuana patients cannot be prosecuted for driving while the drug is in their system. That's the ruling from the Michigan Supreme Court in a unanimous opinion. The court overturned the decision of an appeals court in the case of a northern Michigan man stopped for speeding three years ago. He was charged with driving under the influence of the drug after admitting he smoked medical weed a few hours before being pulled over. The man had a valid medical marijuana card.