For decades, the plain smell doctrine allowed law enforcement to use the smell of marijuana, without more, to establish probable cause for warrantless searches of cars.[1] But the times they are changing.

Though still a crime at the federal level, marijuana has now been decriminalized in eighteen states, two territories, and Washington, D.C.[2] Thirty-seven states, four territories, and D.C. allow the use of medical marijuana.[3] Courts in these jurisdictions now have to decide whether the plain smell doctrine is still alive or whether such laws, by making marijuana no longer per se illegal, “undermine this main pillar supporting” the doctrine.[4]

In Commonwealth v. Barr, the Supreme Court of Pennsylvania took on this challenge. The court held that the smell of marijuana can no longer be “a stand-alone [factor], in determining whether the totality of the circumstances established probable cause to permit police to conduct a warrantless search of a vehicle,”[5] with one justice expressing a reservation about “the broader facets of the majority’s pronouncements.”[6] The application of this rule to the actual facts of the case proved to be more divisive, with two out of seven justices dissenting from the majority’s decision to reinstate the trial court’s order suppressing the evidence obtained after conducting the warrantless search.[7]


Three and a half years ago, on a chilly November night, Teri Barr was making a U-turn when Pennsylvania state troopers Edward Prentice and Danielle Heimbach decided to follow her.[8] No criminal activity was observed, but Prentice was coaching Heimbach, and this seemed like a good opportunity for a lesson, because no other vehicles were around.[9] When the car drove through a stop sign, the officers pulled it over, with the trainee Heimbach approaching the passenger side of the vehicle and the lead officer Prentice the driver’s side.[10] Both smelled burnt marijuana, so Prentice asked the driver—Mrs. Barr—to exit the vehicle.[11] The passenger—Timothy Barr, the husband and also the appellant in this case—exclaimed that “no one is getting out of this fucking vehicle.”[12] There was a third person inside the car, “drifting in and out of sleep” on the back seat.[13]

Eventually Prentice moved to search the car, explaining that the plain smell doctrine allowed him to do that.[14] In response, Appellant Barr and his wife both showed him their medical marijuana cards, which gave them the right to possess and vape (though not smoke) marijuana pursuant to Pennsylvania’s medical marijuana law, enacted in 2016.[15]

The troopers nonetheless proceeded with the search, which turned up a Ziploc bag with 0.79 grams of marijuana and a handgun.[16] A further search turned up several unused clear baggies, consistent with “general packaging for drug distribution.”[17]

Procedural History

Based on this search, Appellant Barr was charged with possession of marijuana and with two firearm offenses.[18] Barr moved to suppress the evidence, arguing there was no probable cause to search the car. At his suppression hearing, an expert—also the physician who recommended Barr for the medical marijuana card—testified that “vaping marijuana produces an odor and that there is no difference between the odor of legally vaped and illegally smoked marijuana.”[19] Because the trial court determined that “the troopers conducted a search of a vehicle based solely on the odor of marijuana emanating from that vehicle,” and given that the expert testified that there was no way to distinguish between the smells of smoked and vaped marijuana, the trial court ruled the search unconstitutional and suppressed the evidence.[20] The court did not provide a detailed totality of the circumstances analysis.[21]

The case then went up to an intermediate appellate court, where the panel agreed that “the odor of marijuana does not per se establish probable cause to allow police to conduct a warrantless search of a vehicle.”[22] However, according to the panel, “the smell of marijuana can be a factor in providing . . . probable cause,” and the trial court should have considered additional factors, such as “(1) Trooper Prentice’s training and experience in narcotics investigations; (2) the fact that Trooper Prentice identified the area where the troopers stopped the vehicle as a high crime area; and (3) Appellant’s statements and demeanor throughout the stop.”[23] As a result, the panel concluded, the evidence should not have been suppressed, remanding the case back to the trial court for the totality of the circumstances analysis.[24]

The Ruling

The Pennsylvania Supreme Court agreed with both courts that the plain smell doctrine is incompatible with the medical marijuana law, and as a result it held that the smell of marijuana alone can no longer supply probable cause. It overturned the immediate appellate court, however, in its determination that the case needs to be remanded for reconsideration of the suppression ruling. In other words, the court held that the trial court was right to suppress.  

The plain smell doctrine:

The court began its analysis of the doctrine by stating that “it is indisputable that, prior to the enactment of the [medical marijuana law], the [Controlled Substances Act] rendered marijuana per se illegal . . . to possess.”[25] As a result, at that time, “the odor of marijuana alone [could] be sufficient to establish probable cause to conduct a search.”[26]

In passing the medical marijuana law, however, Pennsylvania’s General Assembly stopped marijuana from being per se illegal, and as such “eliminated this main pillar supporting the ‘plain smell doctrine.’”[27] Because individuals in Pennsylvania can now “legally possess and consume various forms of medical marijuana, including the plant itself . . . the smell of marijuana alone cannot create probable cause to justify a search under the state and federal constitutions.”[28] The court pointed out that this holding is in line with the court’s precedent on the concealed carry of firearms. In Commonwealth v. Hicks,[29] defendant was seized at gunpoint, removed from his car, and restrained based solely on his possession of a concealed firearm.[30] Because he had a license to possess and carry, the court reversed two lower courts to hold that since the carry of the weapon is not per se illegal, this fact alone cannot be used to justify a Terry stop.[31] The central idea in the Hicks ruling is that lawful activity cannot alone be the basis of reasonable suspicion or probable cause.[32] This same idea, in the court’s view, applies  in the case of marijuana: “[O]ne’s liberty may not be abridged on the sole basis that a law enforcement officer detected the smell of marijuana, because, to do so, would eliminate individualized suspicion required for probable cause.”[33]

The court emphasized, however, that “the smell of marijuana indisputably can still signal the possibility of criminal activity.”[34] After all, “a particular factor contributing to probable cause may involve legal conduct . . . so long as the factor is considered along with other factors that, in combination, suggest that criminal activity is afoot.”[35]

The suppression ruling:

While the court agreed with the appellate court panel that smell alone can no longer supply probable cause, it overruled the panel’s application of this principle to the facts of the Barr case. It said the trial court properly engaged in the totality of the circumstances analysis for the determination of probable cause in concluding that “the troopers searched the vehicle in question based solely on the odor of marijuana emanating from that vehicle.”[36] Based on this conclusion, the supreme court held the trial court properly ruled that Appellant’s rights were violated during the search and that the evidence then obtained should be suppressed.[37]

Justice Saylor’s concurrence

Justice Thomas Saylor wrote separately to express a reservation. To him, it was not clear whether it is possible “to distinguish between burnt marijuana . . . and legally consumed medical marijuana emanating from a vaporization device.”[38] If it is, then the plain smell doctrine is no longer workable. If it is not, however, then the majority reaches too far, since “when an officer smells burnt marijuana emanating from the interior of a motor vehicle,” it seems “very probable that the illegal act of smoking marijuana has been committed.”[39]

Justice Dougherty concurrence and dissent (joined by Justice Mundy)

Justice Kevin Dougherty also wrote separately. He joined the majority in its holding that the odor of marijuana can no longer be a stand-alone factor in the determination of probable cause.[40] But in his concurrence, Justice Dougherty elaborated on the circumstances in which “the smell of marijuana retains salience in the probable cause analysis.”[41] For example, he wrote, if an officer smells marijuana and also observes that, in violation of the medical marijuana law, “there is no barcode or other identifying information that typically appears on the original packaging from a dispensary, that could be enough to establish probable cause.”[42] Similarly, it is illegal to drive under an influence of controlled substances, so if an officer smells burnt marijuana and there is no one but the driver in the car, there is probable cause to believe that the driver was under the influence and thus violated the law.[43]

In addition, Justice Dougherty dissented from the majority’s suppression ruling. First, according to him, even if the trial court did engage in the totality of the circumstances analysis, it did so incorrectly by looking at whether “the troopers’ subjective reason for searching the car, [their smell of marijuana], surmounted constitutional scrutiny.”[44] Second, in Judge Dougherty’s view, the evidence from the search should not have been suppressed, since, like the intermediate appellate panel, he thought that there were other relevant factors that the trial court did not consider.[45] For example, the trial court overlooked the fact that the trooper’s suspicions increased as Appellant Barr’s behavior became more hostile.[46] Also, the car pulled out of a building known for a number of stolen gun and drug cases.[47] In addition, only two of the three occupants of the car presented their medical marijuana cards. The third person was drifting in and out of sleep in the back.[48]

Justice Mundy’s concurrence and dissent

Justice Sallie Updyke Mundy joined the other justices in concluding that the smell of marijuana can no longer be a stand-alone factor in determining probable cause.[49] But she would not have suppressed the evidence at this stage, since “[t]he trial court’s entire probable cause analysis began and ended” with whether plain smell can be sufficient in supplying it.[50] In Justice Mundy’s view, there was “no assessment of the totality of the circumstances” by the trial court.[51] As such, Justice Mundy, like Justice Dougherty, would have remanded for reconsideration rather than require that the evidence be suppressed.[52]

In the end, all seven justices agreed—with a reservation from Justice Saylor—that the odor of marijuana alone is no longer sufficient to establish probable cause for searching cars. There was a 5-2 split, however, on the suppression ruling. Two justices would have sided with the intermediate court and remanded to the trial court for reconsideration with the orders to explicitly consider the totality of circumstances.

[1] Caren Chesler, A Whiff of Pot Alone No Longer Airtight Probable Cause for Police TO Search Cars In Several States, Washington Post (June 26, 2021),
[2] National Conference of State Legislatures, Cannabis Overview (July 6, 2021),
[3] National Conference of State Legislatures, State Medical Cannabis Laws (Feb. 3, 2022),
[4] Commonwealth v. Barr, 266 A.3d 25, 41 (Pa. 2021).
[5] Id.
[6] Id. at 45.
[7] Id. at 46–49.
[8] Id. at 29.
[9] Id.
[10] Id.
[11] Id. at 30.
[12] Id.
[13] Id. at 29.
[14] Id. at 30.
[15] Id.
[16] Id.
[17] Id.
[18] Id. at 29.
[19] Id. at 31.
[20] Id. at 32.
[21] Id.
[22] Id.
[23] Id. at 34.
[24] Id.
[25] Id. at 40.
[26] Id. at 41.
[27] Id.
[28] Id.
[29] 208 A.3d 916 (Pa. 2019).
[30] Barr, 266 A.3d 25 at 42.
[31] Id. at 41–42.
[32] Id. at 42.
[33] Id. at 44.
[34] Id. at 41.
[35] Id. at 41–42.
[36] Id. at 43.
[37] Id. at 44.
[38] Id. at 45.
[39] Id.
[40] Id.
[41] Id.
[42] Id. at 46.
[43] Id. at 47.
[44] Id. at 48 (emphasis added).
[45] Id.
[46] Id.
[47] Id.
[48] Id.
[49] Id.
[50] Id. at 49.
[51] Id. at 49.
[52] Id. at 48, 49.



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