Drugged driving cases in Michigan are often more complicated than alcohol-related OWI cases. Alcohol testing has its own problems, but the legal system has spent decades building procedures around breath testing, blood alcohol analysis, and standardized field sobriety testing. Drugged driving cases do not fit as neatly into that framework. A breath test does not measure THC, prescription medication, opioids, benzodiazepines, stimulants, or other controlled substances. A blood test may show that a drug was present, but presence is not the same as impairment. Field sobriety tests were developed primarily around alcohol impairment, not around the wide variety of legal and illegal substances that may appear in a toxicology report.
When I evaluate a Michigan drugged driving case, I do not begin with the assumption that a chemical test answers the legal question. The central issue is usually whether the prosecutor can prove that the driver was actually under the influence of a controlled substance, another intoxicating substance, or a combination of substances at the time of driving. That question requires careful attention to the driving, the stop, the officer’s observations, the field sobriety testing, any statements made by the driver, the toxicology result, and the scientific limits of interpreting that result.
Michigan’s Drugged Driving Statute
Michigan’s principal operating while intoxicated statute, MCL 257.625(1)(a), prohibits a person from operating a motor vehicle while under the influence of alcoholic liquor, a controlled substance, another intoxicating substance, or a combination of those substances. This provision focuses on impairment. It requires more than proof that a person used a substance at some earlier point. The relevant legal question is whether the person was under the influence while operating the vehicle.
Michigan also has a separate per se provision, MCL 257.625(8), which prohibits operating with any amount of a Schedule 1 controlled substance or cocaine in the body. That provision can be severe because it does not require proof of impairment in the ordinary sense. But marijuana cases require additional care. In People v Koon, 494 Mich 1 (2013), the Michigan Supreme Court held that the per se provision does not apply to a registered medical marijuana patient. Since then, Michigan law has continued to evolve through the Michigan Regulation and Taxation of Marihuana Act, MCL 333.27951 et seq., which generally decriminalized adult recreational marijuana use.
The point is not that marijuana-impaired driving is lawful. It is not. MCL 333.27954 prohibits operating a vehicle “under the influence of marihuana.” The point is narrower and more important in court: Michigan does not punish a lawful adult user merely because THC is detected in the body. The prosecution must prove the statutory offense charged. In marijuana-related driving cases, that often means confronting the difference between use, presence, and impairment.
Why THC Cases Are Different
Alcohol and THC are not scientifically interchangeable. In alcohol cases, prosecutors often rely on a numerical blood alcohol result and ask the jury to treat the number as a proxy for impairment or unlawful operation. THC does not work that way. The Michigan Impaired Driving Safety Commission was created to study whether Michigan should adopt a scientifically supported per se threshold for delta-9 THC. In its March 2019 report, the Commission concluded that there is no scientifically supported threshold of delta-9 THC bodily content that indicates impaired driving. The Commission recognized the poor correlation between driving impairment and blood plasma levels of delta-9 THC at the time of blood collection.
That conclusion matters in real cases. A person may have THC in the blood because of prior marijuana use, but the number may not reliably show whether the person was impaired when driving. The timing of use, route of administration, tolerance, metabolism, blood collection delay, and the distinction between active and inactive metabolites can all affect interpretation. A toxicology report may be important evidence, but it is not a shortcut around proof.
NHTSA’s July 2017 report, Marijuana-Impaired Driving: A Report to Congress, likewise acknowledged that marijuana-impaired driving cannot be detected with the same scientific reliability as alcohol-impaired driving. That is one reason I am cautious when police reports use alcohol-based language to describe a drug case. The fact that a person looks “impaired” to an officer may require careful examination, especially where fatigue, anxiety, medical conditions, lawful prescriptions, balance problems, poor instructions, or environmental conditions may explain what the officer observed.
Field Sobriety Tests in Drugged Driving Cases
Standardized field sobriety tests are commonly used in Michigan OWI investigations. The familiar battery includes the horizontal gaze nystagmus test, the walk-and-turn test, and the one-leg stand test. These tests were developed and validated for alcohol-related investigations. They were not designed to identify every type of drug impairment, and they were not designed to determine whether a particular drug caused impaired driving.
This distinction becomes especially important in marijuana cases. A driver may perform poorly on a divided-attention task for reasons unrelated to marijuana impairment. Roadside testing often occurs at night, near traffic, in poor weather, on uneven pavement, under flashing emergency lights, and after the person has just been stopped by the police. Some people have orthopedic limitations. Some have neurological conditions. Some are simply nervous. The 2023 randomized clinical trial published in JAMA Psychiatry by Marcotte and colleagues adds to the concern by reporting that completely sober subjects frequently failed standardized field sobriety tests. That does not make the tests irrelevant in every case, but it does mean their significance must be examined carefully.
I also distinguish physical performance evidence from testimonial evidence. A person’s balance, coordination, gait, and physical performance are generally treated differently from compelled statements. In many cases, field sobriety testing is analyzed as physical evidence rather than testimonial evidence. That distinction matters because the constitutional issues are not the same. A defense challenge should be tailored to the actual facts, including whether the officer had reasonable suspicion to extend the stop, whether the person was effectively detained beyond the lawful scope of the traffic investigation, whether Miranda issues arose, and whether any refusal evidence or statements are being used improperly.
The Drug Recognition Expert Protocol
Drugged driving cases frequently involve the Drug Recognition Expert protocol, often called the DRE protocol. The protocol is a twelve-step process developed by the Los Angeles Police Department in the 1970s, later adapted by NHTSA, and administered nationally through the International Association of Chiefs of Police. The DRE process purports to allow a trained officer to determine whether a person is impaired by drugs and, if so, to identify the category or categories of drugs involved.
The twelve steps include a breath alcohol test, an interview of the arresting officer, a preliminary examination and pulse, eye examinations, divided-attention tests, vital signs, pupil measurements under different lighting conditions, checks of muscle tone, inspection for injection sites, suspect statements, the evaluator’s opinion, and toxicological testing. On paper, that structure may appear systematic. In practice, the critical issue is whether the method is scientifically reliable and whether the officer applied it reliably in the case being litigated.
One of the recurring criticisms of DRE methodology is circular reasoning. The officer begins with roadside observations and field sobriety testing. If alcohol is not the explanation, the officer looks for signs associated with drug categories. If toxicology later finds a drug in the predicted category, the prediction is treated as confirmed. If toxicology finds another drug, the case may still be argued as drug-impaired because some drug was present. That approach can blur the difference between detecting drug presence and proving drug-caused impairment at the time of driving.
People v Bowden and DRE Testimony in Michigan
The leading Michigan case on DRE testimony in marijuana-impaired driving prosecutions is People v Bowden, 344 Mich App 171 (2022). In that case, the defendant was charged with operating while intoxicated after a traffic stop in Ottawa County. A deputy performed the twelve-step DRE protocol and opined that the defendant was impaired by cannabis to a degree that made it unsafe and unlawful for her to operate a vehicle. The prosecution sought to qualify the deputy as an expert witness. The trial court allowed the testimony, and the circuit court affirmed.
The Michigan Court of Appeals reversed in a published decision. The Court held that the trial court abused its discretion by admitting the DRE testimony under MRE 702. The Court analyzed reliability under principles drawn from Daubert v Merrell Dow Pharmaceuticals, Inc, 509 US 579 (1993), as adopted in Michigan by Gilbert v DaimlerChrysler Corp, 470 Mich 749 (2004). Under MRE 702, the trial court must act as a gatekeeper. Expert testimony must be based on sufficient facts or data, must be the product of reliable principles and methods, and must reflect reliable application of those principles and methods to the facts of the case.
Bowden is significant because it rejects the assumption that DRE testimony is automatically admissible simply because the officer completed training or followed a checklist. In a marijuana case, the prosecution must still establish scientific reliability. A badge, a certificate, and a protocol do not replace the evidentiary foundation required by MRE 702. For defense lawyers, Bowden provides a framework for challenging DRE opinion testimony when the prosecution attempts to present a police officer’s conclusion as scientific proof of cannabis impairment.
Marijuana Odor, Vehicle Searches, and Probable Cause
Drugged driving defense often begins before toxicology and expert testimony. It begins with the stop, the detention, the search, and the blood draw. The smell of marijuana has historically been used by police as a justification for expanding traffic stops and searching vehicles. Michigan law has changed. In People v Armstrong, 344 Mich App 286 (2022), the Court of Appeals held that marijuana odor remains relevant to the totality of the circumstances, but smell alone does not necessarily establish probable cause unless combined with other facts suggesting illegal activity. The Michigan Supreme Court later addressed the issue in People v Armstrong, ___ Mich ___ (2025) (Docket No. 165233), overruling People v Kazmierczak, 461 Mich 411 (2000), and holding that the smell of marijuana by itself no longer provides sufficient probable cause to search a vehicle.
That development matters because marijuana is no longer contraband in the same way it was before Michigan voters approved adult-use legalization. A lawful substance can still be involved in an unlawful driving offense, but police must justify each stage of the encounter. A valid traffic stop does not automatically justify a prolonged roadside investigation. A lawful detention does not automatically justify a search. A search does not automatically justify a blood draw. Each step must be analyzed separately.
Blood Testing and Toxicology Interpretation
Blood testing is often presented as the most objective part of a drugged driving case. It may be objective in the sense that a laboratory instrument produced a result, but interpretation remains a separate issue. A toxicology report may identify a substance, quantify a substance, report a result below the limit of quantitation, or detect a substance without reliable quantification. Those distinctions matter.
In my practice, I look closely at what was actually reported. Was the drug quantified? Was it reported as present below the laboratory’s limit of quantitation? Was an inactive metabolite reported? Was the reported substance consistent with a lawful prescription? Was the blood drawn long after driving? Was there evidence of recent use? Did the laboratory test for the relevant compounds? Were the chain of custody, method validation, calibration, quality controls, and uncertainty issues properly documented? These are not technical distractions. They go directly to whether the prosecution can prove impairment beyond a reasonable doubt.
How I Evaluate a Michigan Drugged Driving Case
A careful defense review begins with the police reports, patrol video, body camera video, dispatch records, implied consent paperwork, warrant materials, blood draw documentation, toxicology packet, and DRE materials if a DRE evaluation was performed. I want to know what the officer observed before the stop, what legal basis existed for the stop, what facts allegedly justified extending the investigation, what instructions were given during testing, and whether the officer’s conclusions are supported by the video.
I also compare the claimed signs of impairment against the drug category alleged by the prosecution. Different drug classes may produce different expected signs. Stimulants, depressants, cannabis, narcotic analgesics, dissociative anesthetics, inhalants, and hallucinogens are not interchangeable. A generic claim that the driver was “impaired by drugs” may conceal weak proof about which drug caused what observed impairment.
When a DRE opinion is offered, I evaluate whether Bowden applies, whether the testimony is being offered as expert testimony, whether MRE 702 has been satisfied, and whether the court should limit or exclude the opinion. When marijuana is involved, I evaluate the case in light of Koon, the MRTMA, the Impaired Driving Safety Commission’s 2019 report, NHTSA’s 2017 discussion of marijuana-impaired driving, and the developing Michigan law on marijuana odor and probable cause.
Conclusion
Michigan drugged driving defense requires more than reading a toxicology number from a laboratory report. These cases require a disciplined review of constitutional procedure, statutory elements, roadside testing, DRE methodology, toxicology, pharmacology, and evidentiary admissibility. The prosecution must prove the offense charged. Presence is not always impairment. Suspicion is not always probable cause. A protocol is not always reliable science. A police opinion is not automatically admissible expert testimony.
When I evaluate a Michigan drugged driving case, I focus on the details that determine whether the evidence is legally admissible, scientifically meaningful, and strong enough to prove impairment at the time of driving. That kind of review is especially important in marijuana cases, prescription medication cases, and cases involving trace or poorly quantified toxicology results. The law in this area continues to develop, and each case must be examined on its own facts, with careful attention to both Michigan law and the scientific limits of drug-impaired driving evidence.
