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Ooh, That Smell, Can't You Smell That Smell?

The Smell of Marijuana and the Fourth Amendment of the Constitution

Jon L. McCurley

Managing Attorney, McCurley Law Firm




The story of marijuana in the United States is complex, full of political maneuvering and conflicting viewpoints. In the 1930s, the Marihuana Tax Act was struck down in Leary v. United States; the law was unconstitutional because it violated Leary’s Fifth Amendment rights.¹ The Court's decision effectively nullified the Marihuana Tax Act.²

The country was deeply divided in the 1970s during the Nixon administration, with high tensions between the government and various groups such as blacks and anti-war leftists, commonly known as “hippies.” Despite the inability to make it illegal to be Black or against the war, Nixon found a way to crack down on his perceived enemies by making marijuana illegal.³ Congress subsequently passed the Controlled Substances Act in 1970 to address drug possession and trafficking. This decision went against the recommendations of several commissions, including the Le Dain Commission,⁵ the British Wootton Report,and the US Shaffer Report.⁷

The plant Cannabis Sativa L, or “marihuana,”is politicized, criminalized, and stigmatized, which can have far-reaching implications. The Controlled Substances Act classified Cannabis as a Schedule I drug, which are determined to have a high potential for abuse and no accepted medical use, prohibiting its use for any purpose.The potent smell of marijuana makes it (and anyone near the plant) an easy target for government surveillance, continuing to circumvent constitutional protections such as the Fourth Amendment.

I. H.B. 1325

In simple terms, the Constitution, through the Fourth Amendment, protects people from unreasonable searches and seizures by the government.¹⁰ The Fourth Amendment, however, is not a guarantee against all searches and seizures, but only those deemed unreasonable under the law.¹¹ This protection is critical, as the smell of marijuana is used as the basis for police searches.¹² Before the passage of Texas House Bill 1325 (H.B. 1325), courts held that the smell of marijuana was sufficient to constitute probable cause to search a person or vehicle.¹³ Since the passage of H.B. 1325, this is not always the case.

In June 2019, H.B. 1325 was signed into law by Governor Abbott. As a result, sections 481.002(5) and 481.002(26) of the Health and Safety Code, were amended as follows:

(5) “Controlled substance” means a substance, including a drug, an adulterant, and a dilutant, listed in

Schedules I through V or Penalty Group 1, 1-A, 2, 2-A, 3, or 4. The term includes the aggregate weight of

any mixture, solution, or other substance containing a controlled substance. The term does not include

hemp, as defined by Section 121.001, Agriculture Code, or the tetrahydrocannabinol in hemp.

(26) “Marihuana” means the plant Cannabis sativa L., whether growing or not, the seeds of that plant,

and every compound, manufacture, salt, derivative, mixture, or preparation of that plant or its seeds. The

term does not include:

. . . .

(F) hemp, as that term is defined by Section 121.001, Agriculture Code.¹⁴

Section 121.001, of the Agriculture Code defines “hemp” as “the plant Cannabis sativa L. and any part of that plant, including the seeds of the plant and all derivates, extracts, cannabinoids, isomers, acids, salts, and salts of isomers, whether growing or not, with delta-9 tetrahydrocannabinol (THC) concentration of not more than 0.3 percent on a dry weight basis.”

H.B. 1325 legalized industrial hemp production. Hemp, a chemotype of the species Cannabis sativa L., as defined by H.B. 1325, can now be legally grown and sold by licensed parties.¹⁵ H.B. 1325 specifically excludes industrial hemp from the definition of marijuana, which remains a controlled substance.¹⁶ Hemp, as defined in H.B. 1325, is not a controlled substance and may be lawfully possessed by any state citizen.¹⁷

Before H.B. 1325, marijuana’s distinct and readily recognizable odor often lead law enforcement to believe that a criminal act was occurring.¹⁸ However, after H.B. 1325 simply detecting the odor of marijuana may not be enough to justify a search or seizure under the Fourth Amendment because in order to search or get a warrant, law enforcement officials must have probable cause that a crime has been committed or is about to be committed.¹⁹ “We’re trained to recognize marijuana. Coming from someone who’s been around hemp as well, they are very similar. They look the same; they smell the same,” said Officer Jeffrey Pearce with the College Station Police Department.²⁰

In a memorandum dated July 10, 2019, Randall Prince of the Texas Department of Public Safety raised concerns about law enforcement and marijuana.²¹ He correctly stated that “marihuana” was not decriminalized.²² According to Deputy Director Prince, DPS crime labs could not measure the THC concentration level in marijuana or hemp.²³ He did, however, say that H.B. 1325 would not restrict officers from enforcing marijuana laws, but did elaborate that “regulatory hemp program[s]” were not established in H.B. 1325.²⁴ Although the DPS says that the decriminalization²⁵ of hemp would not negate probable cause for marijuana-related offenses, they did say that the legal and regulatory structure for hemp was still in flux.²⁶ The State also provided some guidance on the legality of hemp.²⁷

The Legislature has recently excluded “hemp” as defined by Section 121.001 of the Agriculture Code from the definition of marihuana.²⁸ Because of the similarities in the definitions of marihuana and hemp, the continued viability of the holding that officers and lay witnesses may identify marijuana through their senses alone may be in question.²⁹

II. The smell of marijuana is still a basis for searches, but the courts are pushing back.

Two Pennsylvania courts have made rulings related to the smell of marijuana and whether it establishes probable cause for a search. In Commonwealth v. Barr, the court held that the mere odor of marijuana emanating from a vehicle is insufficient to establish probable cause for a warrantless search.³⁰ The court emphasized that the odor of marijuana does not provide probable cause to believe that a crime has been or is being committed.³¹ The case states that “the odor of marijuana may be a factor, but not a stand-alone one, in evaluating the totality of the circumstances for purposes of determining whether police had probable cause to conduct a warrantless search.”³²

Further, in Commonwealth v. Grooms, the court held that the smell of marijuana alone may not establish probable cause for a search.³³ In that case, the police conducted a warrantless search of a locked, unoccupied, and legally parked vehicle.³⁴ The owner of the vehicle was charged with several possession crimes.³⁵ The Pennsylvania Superior Court vacated the defendant’s sentence holding that the trial court erred in applying a per se rule for establishing probable cause.³⁶

Overall, the Pennsylvania Supreme Court, like other courts, has ruled that the odor of marijuana, in combination with other factors, provides enough evidence to justify a search.³⁷ Yet, other courts have ruled that the odor of marijuana alone does not provide enough evidence to support a search and that other factors, such as the location of the odor, the behavior of the individuals involved, and the quantity of the substance, must be considered.³⁸

In the landmark case of Terry v. Ohio, the U.S. Supreme Court ruled that law enforcement officials may briefly detain a person if they have a reasonable suspicion that the person is involved in criminal activity.³⁹ In Illinois v. Caballes, the U.S. Supreme Court ruled that using a drug-sniffing dog during a routine traffic stop does not violate the Fourth Amendment if the stop is not prolonged.⁴⁰ These court decisions have been used to justify searches based on the odor of marijuana in many cases.

III. Hemp and Reasonable Suspicion

Is the smell of hemp even combined with red eyes and slow speech grounds for reasonable suspicion? “Hemp and cannabis look, feel, and smell the same,” according to Florida Assistant State Attorney Andy Kantor.⁴¹ Both hemp and marijuana are the plant species Cannabis sativa L.⁴² Both include the chemical THC (delta-9 tetrahydrocannabinol, a psychoactive compound in marijuana) and terpenes (the chemicals that give Cannabis its smell).⁴³ Around 150 terpenes have been identified in the Cannabis plant.⁴⁴ The difference between hemp, which can be legally possessed and purchased, and marijuana, which remains a controlled substance under Texas law, is the amount of THC that each contains.⁴⁵ The Texas Department of Agriculture inspects hemp to ensure the THC is less than 0.3% of the sample’s dry weight.⁴⁶

So, what of the smell? A compound smells if it is sufficiently volatile. Cannabis (hemp and marijuana) contains monoterpenes, sesquiterpenes, and diterpenes.⁴⁷ These smells reach receptors in the nose. A molecule induces a specific sense of smell provided that its shape matches a complementary cavity of the receptor, much like when two keys can fit the same lock.⁴⁸ So, all cannabis has the same smell from the presence of terpenes.⁴⁹

Differentiating between hemp and marijuana is increasingly more difficult for law enforcement. The only way to determine if cannabis is hemp or marijuana is to test it and measure its THC level, and currently, there is no field test.⁵⁰

IV. Hemp and Probable Cause

The Fourth Amendment of the United States Constitution protects American citizens from unreasonable searches and seizures by the State.⁵¹ Fourth Amendment case law establishes that illegally obtained evidence is inadmissible even if indicative of criminal activity.⁵² Only evidence that is lawfully obtained is admissible.⁵³ H.B. 1325 legalized hemp.⁵⁴ Marijuana and hemp look and smell the same, so there is likely no way for an officer to establish probable cause to search or seize for marijuana with sight and smell alone.

In Beck v. Ohio, the Supreme Court held that probable cause requires “that at the moment of the arrest an officer have facts and circumstances within their knowledge and of which they had reasonably trustworthy information that are sufficient to warrant a prudent man in believing that the petitioner had committed or was committing an offense.”⁵⁵ Additionally, probable cause requires “more than mere suspicion” but less than evidence that would justify a conviction.⁵⁶ Concerning marijuana and hemp, the sight and smell are indistinguishable; therefore, for the purposes of the Fourth Amendment, insufficient to believe a person is committing an offense.

Legalizing industrial hemp has made a K-9 identification of a controlled substance insufficient to form the basis of probable cause for a search. “A K-9 can't decipher the difference between the scent of hemp and ordinary marijuana. They can come from the same plant. The difference is statutorily created by the legislature at 0.3%,” said Ohio State Highway Patrol Lieutenant Rob Sellers.⁵⁷

K-9s detect the presence of marijuana by smelling terpenes in the substance; since both hemp and marijuana contain the same terpenes, a drug detection canine unit will alert on either substance, incapable of distinguishing between the two.⁵⁸ The olfaction system controls the brain’s ability to smell.⁵⁹ K-9s have a highly developed olfactory system and a larger olfactory epithelium than humans.⁶⁰

After identifying the sight or smell of Cannabis sativa L., an officer may attempt to verify his suspicion using a canine. In Texas, lawful products containing less than 0.3% THC can be legally possessed.⁶¹ Because the K-9 could only detect the presence of Cannabis sativa L. by smelling terpenes, there is no reason to suspect that a person had committed or was committing an offense. And therefore, no probable cause to justify the search.

To confirm whether a person did have marijuana, it would require an unlawful seizure. No field test can differentiate if the plant is hemp or marijuana. The Fourth Amendment protects against the seizure of property absent a warrant or probable cause.⁶² Currently, there is no field test, and the Texas DPS can test for THC, but that is not definitive in determining if a plant is hemp or marijuana. This turns into a “catch-22.” Without a way to distinguish between the different strains of Cannabis, there is no probable cause for the seizure. Without the seizure, there is no way to test the substance. The State cannot constitutionally seize property absent probable cause to test for its legality, as the seizure would require an arbitrary state intrusion.⁶³ Without something more than the sight or smell of cannabis, the lack of probable cause makes the seizure unconstitutional.⁶⁴ Without the seizure, there can be no proof that the substance is not legally owned industrial hemp.

The Fourth Amendment to the Constitution and comparable state constitutional provisions demand that probable cause exist for a search or seizure to be deemed lawful.⁶⁵ As there is no authentic way for the state to differentiate between legal hemp and marijuana, an officer cannot have information “sufficient to warrant a prudent man in believing that the petitioner had committed or was committing an offense” based on sight or smell of the plant Cannabis sativa L. alone.⁶⁶ If an officer has no probable cause to search the individual’s person, vehicle, or home based solely on the smell of what is believed to be Cannabis sativa L., the seizure of the substance is similarly without probable cause, as the officer had no way to determine the substance’s legality without arbitrarily seizing it on the presumption that it was a controlled substance.

The command of the State and Federal constitution requires the accused to receive a fair trial and due process of law.⁶⁷ Allowing admittance of evidence collected through a search without probable cause would unfairly prejudice a defendant because it would violate his rights under the Fourth Amendment of the United States Constitution and Chapter 14 of the Texas Code of Criminal Procedure.⁶⁸

In conclusion, the smell of marijuana has been a complex issue in Fourth Amendment law. While the odor of marijuana may provide enough evidence to justify a search in some cases, it is not enough evidence in and of itself to support a search or seizure. In addition, the legalization of marijuana in several states has raised new questions about the relationship between the odor of marijuana and the Fourth Amendment. The courts will continue to grapple with these complex legal questions in the coming years.


Suggested Citation: Jon McCurley, Ooh, That Smell, Can't You Smell That Smell? The Smell of Marijuana and

the Fourth Amendment of the Constitution, ACCESSIBLE LAW, Summer 2023, at 44.

Ooh, That Smell, The Smell of Marijuana and the Fourth Amendment [Issue 13]
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[1] Leary v. United States, 395 U.S. 6, 52 (1969).

[2] Id.

[3] Tom LoBianco, Report: Aide Says Nixon’s War on Drugs Targeted Blacks, hippies, (March 24, 2016)

[4] Overview of Controlled Substances and Precursor Chemicals: Controlled Substances Act of 1970, Factsheets for USC Environmental Health & Safety, (last visited March 18, 2023).

[5] See John S. Bennet, Le Dain Commission of Inquiry into the Non-Medical Use of Drugs Tables Fourth and Final Report, Can Med Assoc J. (Jan. 5, 1974).

[6] See British Advisory Committee on Drug Dependence, Cannabis: Report by the Advisory Committee on Drug Dependence (1968).

[7] See Gabriel G Nahas & Albert Greenwood, The First Report of the National Commission on Marihuana (1972): Signal of Misunderstanding or Exercise in Ambiguity (Jan. 1974).

[8] The Marihuana Tax Act of 1937 used an alternate spelling of marijuana; therefore, although “marijuana” is preferred, this article will use “marihuana” spelling when consistent the wording of statutes.

[9] Overview of Controlled Substances and Precursor Chemicals, supra note 4.

[10] U.S. Const. amend. IV, § 3.

[11] Id.

[12] See, e.g., Isam v. State, 582 S.W.2d 441, 444 (Tex. Crim. App. 1979) (holding that the odor of marijuana provides sufficient probable cause to justify search of automobile); Moulden v. State, 576 S.W.2d 817, 819–20 (Tex. Crim. App. 1978) (holding that the odor of burnt marihuana in automobile constitutes sufficient probable cause to search overnight bag on floorboard in front of defendant who was a passenger in the vehicle); Ross v. State, 486 S.W.2d 327, 328 (Tex. Crim. App. 1972) (holding that the odor of marihuana on defendant’s person creates sufficient probable cause to search defendant’s pockets) overruled on other grounds by Walters v. State, 359 S.W.3d 212 (Tex. Crim. App. 2011); Hernandez v. State, 867 S.W.2d 900, 907 (Tex. App.—Texarkana 1993, no pet.) (concluding that odor of marijuana provided sufficient probable cause to search truck); Jordan v. State, 394 S.W.3d 58, 64-65 (Tex. App.—Houston [1st Dist.] 2012, pet. ref’d) (citations omitted) (holding that a strong odor of marijuana emanating from a car establishes probable cause to search the car and its occupants).

[13] See id.

[14] Tex. Health & Safety Code Ann. § 481.002(5)(26).

[15] H.B. 1325, 86th Leg., Reg. Sess. (Tex. 2019).

[16] Id.

[17] Id.

[18] See Osbourn v. State, 92 S.W.3d 531, 537 (Tex. Crim. App. 2002) (“While smelling the odor of marihuana smoke may not be an event normally encountered in daily life, it requires limited, if any, expertise to identify.”).

[19] U.S. Const. amend. IV, § 3.

[20] Kathleen Witte, Texas A&M-developed device helps weed out hemp from marijuana, KBTX (Jan. 21, 2020, 5:39 PM CST),

[21] Memorandum from Randell Prince, Deputy Director to All Commissioned Personnel (June 10, 2019) (on file with the Department of Public Safety Interoffice).

[23] Id.

[24] Id.

[25] It should be noted that H.B. 1325 legalized hemp, it did not decriminalize it.

[26] Id.

[27] Id. (“HB 1325 does create some criminal offenses related to hemp. The most likely violation encountered by officers is the improper transportation of hemp plant materials. Under section 122.356 of the Agriculture Code, a person is prohibited from transporting these materials, unless they are produced in compliance with an approved hemp program and the person has a shipping certificate or other documentation verifying this information.”).

[28] Tex. Health & Safety Code Ann. § 481.002(26)(F).

[29] Gaffney v. State, No. 06-19-00189-CR, at *6 n.4 (Tex. App. Jan. 29, 2020).

[30] Commonwealth v. Barr, 266 A.3d 25, 41 (Pa. 2021).

[31] Id.

[32] Id. at 41.

[33] Commonwealth v. Grooms, 247 A.3d 31, 41, 2021 PA Super 23.

[34] Id. at 33–35.

[35] Id. at 33.

[36] Id. at 41.

[37] See, e.g., Commonwealth v. Barr, 266 A.3d 25, 41 (Pa. 2021).

[38] See Grooms, 247 A.3d at 41.

[39] Terry v. Ohio, 392 U.S. 1, 20–22 (1968).

[40] Illinois v. Caballes, 543 U.S. 405, 408 (2005).

[42] Cannabis, Leafly, (last visited June 12, 2023).

[43] Sarana Rose Sommano, et al., The Cannabis Terpenes, 24 Molecules (Special Issue) 1 (2020).

[44] Judith K. Bloom & Jörg Bohlmann, Terpenes in Cannabis sativa - From plant genome to humans, 284 Plant Sci. 67, 67 (2019).

[45] Trey Malone, CBD, marijuana and hemp: What is the difference among these cannabis products, and which are legal?, MSUToday (Apr. 6, 2021),

[46] Agriculture and Consumer Protection Division, Tex. Dep’t of Agric., (last visited Apr. 17, 2023); Tex. Agric. Code Ann. § 122.053.

[47] Sommano, et al., supra note 41.

[48] Jennifer C. Brookes, Andrew P. Horsfield & A. Marshall Stoneham, The Swipe Card Model of Odorant Recognition, 12 Sensors 15709, 15709 (2012).

[49] Sommano, et al., supra note 41.

[50] Jolie McCullough, Texas was warned its new hemp law would complicate marijuana prosecutions. Lawmakers didn’t listen., The Tex. Tribune (July 30, 2019, 12AM CST),

[51] U.S. Const. amend. IV, § 3.

[52] See Mapp v. Ohio, 367 U.S. 643 (1961).

[53] Id.

[54] H.B. 1325, 86th Leg., Reg. Sess. (Tex. 2019).

[55] Beck v. State of Ohio, 379 U.S. 89 (1964).

[57] Lacey Crisp, Hemp or marijuana: Can police K-9’s sniff out the difference?, 10 WBNS (Aug. 22, 2019, 4:14 PM EDT),

[58] Jeff Welty, The Effect of Legal Hemp on Drug Dog Sniffs (Part I), N. C. Criminal Law: A UNC Sch. of Gov’t Blog (Feb. 6, 2023),

[59] Colleen Walsh, What the nose knows, The Harvard Gazette (Feb. 27, 2020),

[60] Eileen K. Jenkins, Mallory T. DeChant, & Erin B. Perry, When the Nose Doesn’t Know: Canine Olfactory Function Associated With Health, Management, and Potential Links to Microbiota, Frontiers in Veterinary Sci., Mar. 2018, at 4.

[61] See H.B. 1325, 86th Leg., Reg. Sess. (Tex. 2019).

[62] U.S. Const. amend. IV, § 3.

[65] U.S. Const. amend. IV, § 3; Tex. Const. art I, § 9.

[66] Beck v. State of Ohio, 379 U.S. 89, 92 (1964).

[68] U.S. Const. amend. IV, § 3; Tex. Code Crim. Proc. § 14.03.



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