Michigan Court Allows Medical Marijuana Users to Drive if Not Impaired
A Michigan Supreme Court ruling confirms registered medical marijuana patients can legally drive after using the drug, provided they are not considered 'under the influence.'
The Michigan Supreme Court ruled this week that registered medical marijuana patients are permitted to drive after using the drug, as long as they are not proven to be impaired while behind the wheel. The decision clarifies a legal conflict that has affected drivers since the state legalised medical marijuana in 2008.
The case centred on Rodney Koon, a registered patient who was stopped for speeding in Grand Traverse County in 2010. Koon admitted to having smoked marijuana earlier in the day, and a subsequent blood test confirmed the presence of the drug. Despite Michigan’s zero-tolerance policy for non-medical users, the Supreme Court found that the state’s medical marijuana law protects registered patients from prosecution based solely on the presence of marijuana in their system.
The unanimous verdict overturned an earlier appeals court decision, which had left Koon at risk of conviction. The Supreme Court stated that while the law prohibits driving 'under the influence' of marijuana, it does not define what level of the drug constitutes impairment. This absence of a statutory threshold means police must demonstrate actual impairment, rather than rely on blood test results alone.
No clear definition of 'under the influence'
Michigan’s medical marijuana law was described by the justices as 'imperfect', noting that repeated court interventions have been necessary to clarify its application. The law shields registered patients from prosecution for internal possession, but leaves ambiguity around what constitutes being 'under the influence' while driving. Without a defined limit, law enforcement must rely on observations of impairment, such as erratic driving or failed sobriety tests, to bring charges against a medical marijuana user.
Implications for drivers and law enforcement
For registered medical marijuana patients, the ruling provides legal clarity: they cannot be prosecuted for driving with traces of marijuana in their system unless police can prove impairment at the time of driving. For law enforcement, the lack of a defined THC threshold complicates prosecution and places greater emphasis on field observations and evidence of diminished driving ability.
The Supreme Court acknowledged the law’s shortcomings and indicated that legislative action would be needed to establish a clear standard for marijuana impairment. Until then, the burden remains on police and prosecutors to show that a medical marijuana user was actually 'under the influence' when stopped.
This ruling does not affect Michigan’s zero-tolerance approach for non-medical users, who remain subject to prosecution if any trace of marijuana is detected while driving.
