Last verified: April 2026
The Statute — MCL 257.625
Michigan Vehicle Code § 257.625 makes it illegal to operate a motor vehicle while “under the influence” of a controlled substance. Subsection (8) historically imposed a zero-tolerance per se rule: any amount of a Schedule 1 substance — including THC — in the driver’s body was per se illegal.
People v. Koon (2013) — The Medical-Patient Carve-Out
In People v. Rodney Lee Koon, decided unanimously by the Michigan Supreme Court on May 21, 2013, the court held that the Michigan Medical Marihuana Act (MMMA) supersedes the zero-tolerance rule for registered medical patients. Quoting the court:
“The MMMA is inconsistent with, and therefore supersedes, MCL 257.625(8) unless a registered qualifying patient loses immunity because of his or her failure to act in accordance with the MMMA.”
The court declined to define “under the influence” with a numerical threshold, holding only that the term “contemplates something more than having any amount of marijuana in one’s system and requires some effect on the person.” This left a substantial discretionary zone for prosecutors and defense attorneys to argue impairment in individual cases — an environment that produces inconsistent outcomes across counties.
For Non-Medical Adult-Use Consumers
For non-medical adult-use consumers, the law is murkier. The literal text of § 257.625(8) still imposes zero tolerance for THC, but Michigan prosecutors and the State Police generally pursue impairment-based prosecutions under § 257.625(1)(a). A 2019 amendment removed inert THC metabolites from the prohibited-substance list. The practical takeaway for Detroiters:
- Do not drive with detectable THC.
- Never assume MRTMA gives the same DUI shield that the MMMA does — Koon’s holding is specifically tied to the MMMA’s qualifying patient status, not to MRTMA’s general adult-use legalization.
The Drug Recognition Expert (DRE) Protocol
Michigan law enforcement uses the standard 12-step Drug Recognition Expert protocol: pulse, blood pressure, eye examinations (horizontal gaze nystagmus, vertical gaze nystagmus, lack of convergence), pupil-size measurements in three lighting conditions, divided-attention tests (one-leg stand, walk-and-turn, finger-to-nose), psychophysical evaluation, and toxicological confirmation. The protocol was developed for general drug-recognition and applies to cannabis impairment in addition to other drugs.
The reliability of DRE evidence in cannabis cases is contested. Cannabis impairment does not produce the same characteristic ocular or motor markers as alcohol or other CNS depressants. Defense attorneys regularly challenge DRE testimony at trial.
Penalties
A first-offense conviction under MCL 257.625 carries:
- Misdemeanor classification
- Fine of $100–$500
- Up to 93 days in jail (or 360 hours community service for OWVI offense)
- Driver’s license suspension
- Six points on the driving record
- Possible vehicle immobilization
- Substance-abuse evaluation
Repeat offenses escalate; a third offense within a lifetime is a felony.
Open-Container Rule
Cannabis in a vehicle must be in a sealed container in the trunk or in a non-passenger area. Open containers in the passenger compartment can support a traffic-stop search. The smell of burnt cannabis can be one factor in a roadside DUI determination; the smell of unburnt cannabis alone is more contested in Michigan and may not, by itself, support a vehicle search.
Federal Driving — CDL Holders
Commercial driver’s license (CDL) holders — bus drivers, truck drivers, school-bus drivers, and similar positions — are governed by Federal Motor Carrier Safety Administration (FMCSA) Part 382 drug-testing rules. Federal rules impose zero tolerance for cannabis. A failed drug test triggers Substance Abuse Professional (SAP) evaluation, CDL Clearinghouse reporting under the Drug & Alcohol Clearinghouse, and disqualification from CDL operation. State legalization does not affect this. Detroit’s logistics workforce — the Ambassador Bridge alone recorded 1.9 million commercial truck crossings in 2025 — operates entirely under FMCSA’s zero-tolerance regime.
Practical Advice for Detroit Drivers
- Do not drive after consuming cannabis — even hours after, depending on tolerance and consumption method.
- Store cannabis in the trunk or sealed in a non-passenger compartment — not in the passenger compartment.
- Do not consume in a vehicle — whether parked or moving, on public roads or in a private parking lot, this is prohibited.
- Be aware of jurisdictional borders. Crossing into Ohio, Indiana, or any neighboring state subjects you to that state’s DUI rules.
- For CDL holders, do not consume at all.
For in-depth cannabis education, dosing guides, safety information, and research summaries, visit our partner site TryCannabis.org
Related on this site: Michigan Civil Asset Forfeiture, Detroit Home Grow & Detroit Home..., MRTMA & the 2018 Vote.