Marijuana Legalization Regimes and the Evolving Fourth Amendment

Posted in: Constitutional Law

Glance at any Criminal Investigation casebook, treatise, or law student outline and it is immediately apparent that the Fourth Amendment rules that govern police searches and seizures have been built up around vice crimes. Drug crimes in particular have played a leading role in the development of doctrines that limit police intrusions into personal privacy. The last decade has seen a dramatic change in drug laws, especially in marijuana laws that account for almost half of all drug arrests. These changes have further complicated an already-tangled skein of Fourth Amendment rules, raising new questions about whether and how police practices will evolve.

In this column, I will first review how marijuana laws in the United States have changed over time, from the earliest criminalization of marijuana by the states to its recent decriminalization in some states. I will then highlight the resulting doctrinal uncertainty by outlining the different ways states have applied the Fourth Amendment’s “automobile exception” in cases involving marijuana and by raising questions about the doctrines governing police canines. I conclude that this doctrinal uncertainty should trigger legislative or judicial scrutiny and intervention to clarify how police practices should be revised.

A Shifting Legal Backdrop

Before turning to some of the doctrinal challenges, let’s see just how much marijuana laws have changed. Just over 100 years ago, Massachusetts became the first state in the union to criminalize marijuana. Other states followed suit, and the federal government got on board in 1937. Seventy years later, Oregon introduced decriminalization, classifying possession of small amounts of marijuana as merely a civil infraction. In 1991, San Francisco became the first city to pass an ordinance permitting medical marijuana, and state medical marijuana laws followed in the late 1990s. Today, 21 states and the District of Columbia have medical marijuana regimes, sixteen states have either decriminalized marijuana (making it a civil infraction) or consider possession a criminal infraction that cannot result in jail time, and two states (Colorado and Washington) have completely legalized possession of limited quantities. Twenty-three states still criminalize all instances of marijuana possession.

The existing approaches can be broken down into four distinct categories:

  • Possession can be perfectly legal;
  • It can be a civil infraction, punishable by a fine (like getting a traffic ticket);
  • It can be criminal, punishable only by a fine; or
  • It can be criminal, punishable by jail time.

Determining which category applies in any particular state depends on:

  • The person’s individual characteristics (age, medical marijuana prescription, etc.);
  • The location where the activity takes place; and
  • The amount of marijuana involved.

The lack of consistency between the states further complicates the picture. For example, it is now perfectly legal in Colorado for someone over the age of 21 to possess up to an ounce of marijuana. The same is true in Washington, except that consuming marijuana in public is a civil infraction. In both states, it is a misdemeanor to possess more than an ounce, but in Colorado felony charges kick in at 12 ounces while in Washington felony possession starts at about 1.4 ounces (40 grams). Other states consider possession of a small amount of marijuana a civil infraction, but the amounts differ widely, from 0.5 ounces in Connecticut and North Carolina to 2.5 ounces in Maine. Possession of more than that amount remains criminalized, with further disagreement about the distinction between misdemeanor and felony possession.

In light of this tangled web of marijuana laws, there is a great deal of uncertainty about how exactly the constitutional rules that govern policing might change. Like marijuana regulation itself, states will—and already have—adopt different interpretations of Fourth Amendment rules.

Warrantless Vehicle Searches

As a general rule, the Fourth Amendment requires police to obtain a warrant before searching. That rule, however, is riddled with exceptions. In Carroll v. United States, a Prohibition-era bootlegging case, the Supreme Court created the “automobile exception” to the warrant requirement. After Carroll, a police officer who has “probable cause for believing that [a] vehicle[is] carrying contraband” can conduct a search of a vehicle without bothering to get a warrant. Back when marijuana was illegal, things were pretty straightforward: an officer who approached a vehicle and smelled marijuana could search the vehicle. Unfortunately, the Supreme Court hasn’t gotten around to clarifying how the automobile exception applies given the change in marijuana laws. State courts have, and their conclusions have been predictably inconsistent.

Some state courts have held that, because possession of some amount of marijuana remains criminalized, the automobile exception applies whenever officers smell marijuana in a vehicle. A recent California case took this approach, holding that an officer who smelled marijuana could conduct a warrantless vehicle search—even though the driver held a prescription for medical marijuana—because the officer “was entitled to investigate to determine whether [the driver] possessed marijuana for personal medical needs.” Although marijuana is almost certainly treated differently than other medicines (would the court have come to the same conclusion had the driver presented a prescription for valium or oxycodone after the officer observed a pill in plain sight?), the rule allows police to proceed as they did before: Smelling marijuana in a vehicle means they can conduct a warrantless search to investigate a potential criminal violation..

Other states have also applied the automobile exception whenever officers smell marijuana, but for a very different reason. Under Camara v. Municipal Court, the Fourth Amendment applies to both criminal and non-criminal searches, and some courts have concluded—sometimes implicitly—that the automobile exception is not limited to criminal investigations. Under Maine Supreme Court precedent, for example, a police officer who smells the odor of marijuana coming from a vehicle has probable cause to believe that a civil infraction is being committed and can therefore conduct a warrantless search of the vehicle to investigate and enforce the civil infraction. So officers who smell marijuana still get an automatic warrantless search, but primarily for regulatory, not criminal, purposes.

Yet other states have held that the automobile exception does not automatically apply when officers smell marijuana. Concluding that the automobile exception applies only when officers have probable cause to believe that a crime has taken place, Massachusetts courts have held that an officer can conduct a warrantless search only when there is “probable cause to believe a criminal amount of contraband [is] present.” In the future, we can expect probable cause determinations to be hotly litigated. Does a “faint odor of marijuana” establish probable cause? What if an officer testifies that drug traffickers are known to use packaging techniques that minimize odor? Can the smell of burnt marijuana ever establish probable cause? What will experts say about how characteristics like quantity, freshness, and environmental factors (temperature and humidity, for example) affect the odor of marijuana?

Police Canines

The automobile exception is not the only area of law unsettled by changing marijuana laws. Another involves police canines, which see frequent use in the drug context for several different reasons. First, a dog sniff doesn’t qualify as a search for Fourth Amendment purposes, which means that no warrant, probable cause, or even particularized suspicion is necessary. Second, when a police canine “hits” on a vehicle or container, it establishes probable cause that can be used to obtain a warrant or conduct a warrantless search (under the automobile exception, for example). Finally, police can use a canine alert on cash to support the conclusion that the cash was associated with criminal activity such as drug trafficking, making the money subject to civil asset forfeiture. Changing marijuana laws call all three doctrines into question.

Would a police canine sniff become a search? A canine sniff isn’t considered a search because the Court has concluded that a police dog ’s schnoz is a well-trained instrument that detects only contraband. People have no legitimate (legally protected) interest in illegal activity, so police actions that reveal only illegal activity simply don’t implicate the Fourth Amendment. In states that have legalized marijuana, however, a police dog that has been trained to alert on marijuana would hit on something that isn’t (necessarily) contraband. The situation may be even worse in terms of Fourth Amendment privacy in states with medical marijuana laws, as canines will alert to something that state law classifies as medicine. If a drug dog can reveal non-criminal information about a person, it may fundamentally change the Fourth Amendment character of police canine sniffs.

When a drug dog that has been trained to hit on marijuana does alert, does it establish probable cause in states that have legalized or decriminalized marijuana? Even if police dogs could be trained to ignore certain strains of (medical) marijuana, the dog certainly wouldn’t know if the occupant of a car or owner of a suitcase has a prescription. Further, drug dogs are not going to be able to distinguish between the smell of almost an ounce of marijuana (entirely legal) and just over an ounce (illegal), even though canines are said to be trained to ignore “micro-residual” smells. If a drug dog could be hitting on a legal substance, courts could very well find that the alert itself does not establish probable cause.

In the civil asset forfeiture context, a canine hit on money is considered strong, though not dispositive, evidence that the cash was involved in illegal activity. Some critics have argued that much of our currency, as much as 80% of bills in circulation, contains trace amounts of illegal drugs, particularly cocaine. Even the word “trace” may be a little dramatic, since studies have estimated that the average bill is host to between 16-millionths of a gram and one-thousandth of a gram of cocaine. Now that marijuana is legal, we can expect to see more trace amounts on currency—remember, it takes only one “badly exposed” bill to contaminate others in the same cash drawer, counting machine, or wallet. As it becomes more common for marijuana residue to be present on bills legally, police canine alerts on money may become less probative.

Finally, it is worth pointing out that smells don’t stop at the state line. Imagine a Coloradan who frequently keeps a legal amount of marijuana in her purse, which she puts in the center console of her vehicle. Cognizant that Utah criminalizes marijuana, she empties her stash before driving over the state line on a business trip. If she’s stopped and the vehicle sniffed, a well-trained dog is almost certain to hit on the vehicle, the purse, and the cash in the purse. Is there probable cause to search the vehicle for a violation of Utah law, keeping in mind that the Court has said that the possibility of an innocent explanation does not obviate a trained officer’s suspicions of criminality?

Perhaps the simplest solution will be for police agencies to use dogs that don’t alert to marijuana, either by training new dogs or “desensitizing” current canines. Some police agencies are doing just that, but here, too, there are no clear legal requirements for officers. In Washington, for example, the Criminal Justice Training Commission no longer requires police canines to be trained to detect marijuana, but continues to certify dogs that are. Prosecutors and defense attorneys alike have raised doubts about desensitization training, but given the expense of acquiring new canines—$8,000 to $10,000 plus recurring expenses for each new canine and “retirement” expenses for the old canines—and the 6- to 9-year working life of a police dog, the period of uncertainty may be prolonged.


Drug laws have played a central role in the development of Fourth Amendment doctrines and law enforcement operations. As the underlying laws change, courts and police agencies will have to adapt. This column examines just two of several areas of constitutional uncertainty, and there are any number of others, from plain smell to search incident to arrest. Police practices that are not governed by constitutional rules will also need to be reviewed. For example, how should police departments store marijuana, a perishable good, that may need to be returned to its owner? And how should police departments deal with marijuana seizures when large volumes are illegal, but small amounts aren’t? (It would seem very odd for police departments to break up big seizures into one-ounce packages and auction them off!) Will a police department in Utah give its seized marijuana to an agency in Colorado to sell?

Doctrinal uncertainty should not lead us automatically to prefer the status quo. It should, however, lead us to think sensibly about how the rules that regulate the police need to accommodate changing drug laws.

Hat tip to James Lewis, a student in my Regulation of Vice seminar and a soon-to-be Baltimore prosecutor, for helpful conversations.

3 responses to “Marijuana Legalization Regimes and the Evolving Fourth Amendment”

  1. MikeParent says:

    Prohibition is only favored by Prohibitionist parasites, who profit from MJs illegality and by the ignorant who blindly believe the lies and propaganda.

  2. jajaeppa says:

    First. .. there are almost 30 states allowing medical. … second. The cops don’t need a warrant to search you your car or your house. … they don’t even need reasonable suspicion. All they need is a reason. .. finding tomato stems from your recent grocery store purchase is good enough for them. . Or seeing you leave a hydro ponic store. .. good enough for them. .. used to be a cop had to investigate before invading someone’s house or self. .. now they don’t care if you even use marijuana. .. they will come in. .. and probably shoot someone. .. Google it if you’re in denial

  3. alb822 says:

    I admit I was against legalization in the 1970s. I’ve done a little more in-depth research since then. I’ve come to the conclusion that the underlying reason for Anslinger’s anti-marijuana mission boils down to money. When he was appointed to the newly created Federal Bureau of Narcotics (FBN) as its first commissioner, his budget was $100,000. The best way to get money out of Congress is to create the need. It doesn’t matter if he had a “hidden agenda” working with DuPont petrochemical interests & William Randolph Hearst creating the highly sensational anti-marijuana campaign to eliminate hemp as an industrial competitor (i.e., Marijuana Tax Act). Maybe he really didn’t consider marijuana a serious threat to American society until 4 yrs. into his tenure (1934), it still became his primary focus as part of the government’s broader push to outlaw all recreational drugs. He completely disregarded as “unscientific” the La Guardia Committee’s detailed study into the effects of smoking marijuana. It systematically contradicted claims made by Treasury that smoking marijuana results in insanity, & determined that the practice of smoking marihuana does *not* lead to addiction in the medical sense of the word. We’re now 70 yrs. behind Isreal reagarding any real research. Also, Australia is known for the highest THC levels (> 40 percent). The US holds a marijuana patent — fyi. An additional consideration: Law Enforcement Against Prohibition (LEAP) (a 501(c)3 composed of current & former law enforcement officers – & others not in law enforcement – who consider current drug policies a failure) favors regulation & control.