State Legalization of Marijuana Is Changing Search and Seizure Jurisprudence

Federal courts have repeatedly held that the smell of marijuana is evidence of criminal activity and justifies a search by law enforcement. But in response to the changing legal status of marijuana, some state courts are reconsidering whether, and under what circumstances, the smell of marijuana can justify government intrusion. Over the past two decades, half of the states enacted laws making it legal for adults to buy and use marijuana for recreational purposes. And roughly 45 states and territories permit adults to use marijuana for medical purposes.

Searches Based on the Smell of Marijuana

The Michigan Supreme Court recently held in People v. Armstrong that the smell of marijuana alone does not justify the warrantless search of a car. In Armstrong, police surrounded a parked car based on one officer’s report that she smelled marijuana coming from the car. Jeffrey Armstrong was in the passenger seat. The officers ordered him out of the car, searched underneath his seat, and found a gun. Armstrong was charged with unlawfully carrying the gun. In a pretrial motion to suppress the gun, he argued it was the fruit of both an unconstitutional seizure and an unconstitutional search: The seizure was unlawful because the smell of marijuana did not establish reasonable suspicion of criminal activity, he said, and the search was unlawful because the only justification for searching the car was the smell of marijuana, which did not establish probable cause to believe the car contained contraband or evidence of a crime.

The government countered that the smell of marijuana provided both reasonable suspicion to justify seizing the car and its occupants and probable cause to justify searching the car under the so-called automobile exception to the warrant requirement. The automobile exception allows law enforcement to search a car without a warrant if they have probable cause to believe it contains contraband or evidence of a crime.

The Michigan Supreme Court rejected the government’s argument and held that the officer’s claim that she smelled marijuana coming from the parked car did not establish probable cause to justify a warrantless search under the automobile exception. The court did not reach the question of whether the smell provided the officers with reasonable suspicion to detain Armstrong.

The court’s decision turned on a 2018 voter-initiated law making it legal for adults aged 21 and over to possess and transport marijuana on their persons and in their cars. “In light of the voters’ intent to legalize marijuana usage and possession, the smell of marijuana, standing alone, no longer constitutes probable cause sufficient to support a search for contraband,” the court wrote, holding that the 2018 law superseded the court’s prior holding that the smell of marijuana alone may establish the requisite probable cause. The court emphasized that probable cause to search depends on the totality of the circumstances and whether law enforcement can demonstrate a reasonable likelihood the search will uncover contraband or evidence of a crime.

The Armstrong court explained that the smell of marijuana, in combination with a driver appearing intoxicated, might establish probable cause to believe the driver was operating under the influence of marijuana, in violation of state law. Similarly, the smell of marijuana, combined with the observation of smoke, might establish probable cause to believe a person is smoking marijuana in public, which remains unlawful in Michigan. In both examples, police need something more than the smell of marijuana to establish probable cause of a crime. 

State courts in Colorado, Illinois, Minnesota, and Pennsylvania have taken a similar approach, acknowledging that the smell of marijuana can be one — but not the only — factor in determining whether the totality of the circumstances establish probable cause to search.

In Michigan, the concept that the smell of marijuana alone does not establish probable cause is not entirely new. Prior to legalizing recreational marijuana use in 2018, Michigan permitted citizens to possess and use marijuana for authorized medical purposes. During that era, the Michigan Court of Appeals grappled with a similar question: whether the smell of marijuana established probable cause to search the car of a driver who was permitted to lawfully possess marijuana under the Michigan Medical Marihuana Act. In a case where the officer smelled marijuana and the driver — who had a permit for medical marijuana — denied having marijuana in his car, the court concluded that there was probable cause to search the car. The court reasoned that it was not the smell of marijuana alone that established probable cause, because it was lawful for the driver to possess marijuana within the limits of the act. Rather, it was the fact that the driver lied about having marijuana that established probable cause to believe he was carrying marijuana in a manner or in quantities that exceeded what was permitted.

In jurisdictions where marijuana possession is now legal for medical or recreational use, courts must reevaluate the relationship between the smell of marijuana and suspected illegal conduct. In states like Michigan, where citizens can lawfully possess and openly transport marijuana in their cars, the smell alone does not suggest any illegal conduct. By contrast, in states like Illinois, where marijuana inside a vehicle must be stored in sealed, odor-proof containers, the smell of marijuana suggests that marijuana is not being stored as required by law. There, the smell alone might support probable cause.

Lingering Legal Questions

Courts must grapple with various other questions when legislatures decriminalize or legalize marijuana. Many states have yet to determine whether the smell of marijuana provides reasonable suspicion for an investigative stop. Under Terry v. Ohio, police may briefly detain a citizen based on reasonable, particularized suspicion that the person is involved in criminal activity. In Armstrong, the Michigan Supreme Court considered this question but ultimately did not reach it because it was not necessary to resolve the case. The few states that have addressed this question have treated it much like the determination of probable cause, holding that the smell of marijuana can be one factor, among others, establishing reasonable suspicion. Several states, including Arizona and Maryland, have enacted legislation prohibiting Terry stops based solely on the smell of marijuana.

Some state courts have grappled with whether suspected marijuana-related civil infractions can serve as the basis for a Terry stop or search, given that the conduct is no longer defined as criminal activity. For example, the Massachusetts high court held that the smell of burnt marijuana cannot establish reasonable suspicion of criminal activity since marijuana is decriminalized in Massachusetts. The Michigan Supreme Court is set to hear oral arguments next month about whether the automobile exception permitted a trooper to search a car where the trooper smelled marijuana and learned the occupants of the car were under the age of 21, where it is a civil infraction to possess marijuana while under the age of 21.

The legalization of marijuana also raises questions regarding the use of drug-detection dogs. Historically, federal courts have not considered the use of drug-detection dogs to be a search. A search occurs when the government intrudes into an area in which an individual has a reasonable expectation of privacy. Federal courts have explained that drug-detection dogs are exclusively trained to alert to illegal drugs, and people do not have a reasonable expectation of privacy in the scent of illegal drugs. But many drug-detection dogs are trained to detect marijuana. Where a state has legalized marijuana, does the use of these dogs constitute a search? In October, the Tennessee Supreme Court will hear oral arguments on a similar question: How does the legalization of hemp affect a probable cause analysis where law enforcement relies, in part, on a positive alert from a drug-detection dog incapable of differentiating between the smell of legal hemp and illegal marijuana?

In Colorado v. McKnight, the Colorado Supreme Court held that, in light of state law legalizing the possession and transportation of small quantities of marijuana, a drug-detection dog trained to alert upon smelling marijuana invades privacy rights. Therefore, drug-detection dogs may only be used in Colorado where law enforcement have probable cause to believe an area contains illegal drugs. 

Conditions of probation may also be ripe for litigation. Recently, the Michigan Supreme Court granted leave to consider whether a statute mandating that probationers follow all federal laws requires trial courts to bar probationers from engaging in marijuana use that is otherwise permitted under Michigan law. The court also asked the parties to address, in the alternative, whether and under what circumstances a trial court may prohibit marijuana use as a discretionary condition of probation.

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Search and seizure jurisprudence may be out of step with laws legalizing marijuana. Practitioners in those jurisdictions should consider challenging government searches, stops, and other actions relating to marijuana smell, possession, and usage. When criminal statutes change, so does the scope of unreasonable government intrusions.

Maya Menlo is an Assistant Defender at the Michigan State Appellate Defender Office, where she represents children and adults on appeal from juvenile court and criminal court proceedings.

Erin Van Campen is a Research & Training Attorney at the Neighborhood Defender Service of Detroit, where she provides on-call assistance and training to public defenders and appointed counsel in Wayne County, Michigan.

Together, they teach Criminal Procedure at Wayne State University Law School.

Suggested Citation: Maya Menlo & Erin Van Campen, State Legalization of Marijuana is Changing Search and Seizure Jurisprudence, Sᴛᴀᴛᴇ Cᴏᴜʀᴛ Rᴇᴘᴏʀᴛ (Sep. 24, 2025), https://statecourtreport.org/our-work/analysis-opinion/state-legalization-marijuana-changing-search-and-seizure-jurisprudence