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A Marijuana Breathalyzer Is Here, But Skepticism Remains High

Created by FindLaw's team of legal writers and editors.

Updated 10/16/19

Police officers commonly use breathalyzer tests during traffic stops when they suspect a driver is drunk. Soon, they may use a similar breath test if they suspect a driver is high.

For years, scientists have been busy working on a breathalyzer device that tests drivers for marijuana impairment. As of September 2019, the first marijuana breathalyzers are here using carbon nanotubes to test the tetrahydrocannabinol (THC molecules) level in breath samples, but questions remain on the validity of the tests.

Marijuana Impairment Is Difficult to Measure

It took decades for alcohol breathalyzers to become accurate and reliable (although some defense attorneys argue that these tests still have a high margin of error), and it appears that breath testing for weed impairment will need its own trial period to address a unique set of concerns. For example:

  • Marijuana stays in a person’s system longer than alcohol does, so it’s not as simple as measuring if or how much marijuana is present. THC, the component in the drug that causes a “high” and leads to impairment, can stay in a person’s body for up to a month, long after any high wears off.
  • Most people agree that the amount of alcohol in a person’s blood directly correlates with how drunk a person is, but the same isn’t necessarily true with marijuana. A person could have a higher THC level based on body type alone, as THC is stored in fat cells.
  • While 0.08 has been determined as the legal limit for blood-alcohol concentration (BAC), it’s not as simple to draw a hard-and-fast line with pot. Even though a few states have enacted laws that attempt to put a limit on how much THC causes impairment, no consensus has been reached on what level is unsafe for driving.

These issues make it difficult to evaluate when a driver is actually impaired by the drug, especially in the growing number of states where there is marijuana legalization, but you cannot drive while stoned.

New Marijuana Breathalyzer Focuses on Timing

In an effort to solve the problem of measuring THC impairment, scientists have created a breath test that focuses on when a person smoked marijuana, which they say research shows is more important than whether or how much THC is in a person’s system.

One device, developed by Dr. Mike Lynn of Oakland-based Hound Labs, tests marijuana use within a specific timeframe, such as a driver smoking weed within the past three hours, which is allegedly when people are most likely to be impaired. According to the company’s website, THC levels become virtually undetectable in the breath after three hours. The University of Pittsburgh also developed a weed breathalyzer to test for the presence of THC that is more accurate than the current standard of using mass spectrometry.

What about edibles, you ask? That would require a whole separate test of saliva.

Other Methods of Testing Marijuana Impairment

Without a breath test, law enforcement is left with other, more subjective and less accurate methods to determine if a driver is high.

Field sobriety testing and observation: Also known as roadside sobriety tests, these tests usually include three parts that allow the officer to evaluate a driver's balance, attentiveness, response time, and other behavior. An officer may also observe a driver for slurred speech, red eyes, and other signs of pot use. These tests can be subjective and may not provide enough evidence on their own to result in a conviction.

Drug-recognition experts: These specially-trained officers, commonly referred to as DREs, use a 12-step process that takes an hour to complete in an effort to determine whether a driver is intoxicated by a drug, and if so, which drug. Officers take a driver’s blood pressure and pulse, as well as perform eye exams and balance tests. Not all courts accept evidence gathered by DREs because they are not medically trained.

Saliva swab tests: Some police departments have begun using mouth swab tests, which use a saliva sample to test for the presence of numerous drugs, including THC. At this point, swab testing has not caught on in the United States as it has in other countries, and concerns have been raised about a high false-positive rate.

Blood, urine, or hair sample tests: These tests can be administered at a hospital or police station, but the tests are invasive, and results can take days or weeks. Human hair can also be found and tested without the owner's consent.  Furthermore, THC stays in the body for much longer than the person is impaired, so they provide little evidence as to whether the driver was impaired at the time of the stop.

As you can see, a more reliable and objective standard for drug testing and evaluating THC impairment was badly needed, especially with medical marijuana and recreational use becoming legal in a growing number of states.

What Are the Legal Implications of Marijuana Breathalyzers?

Because many police departments throughout the country are eager for the technology, it is likely they will start using marijuana breathalyzers to test for recreational marijuana before all the concerns are addressed. That means courts, prosecutors, and criminal defense attorneys will play an important role in evaluating the devices on a case-by-case basis.

If you are charged with a marijuana DUI, it will be extremely important to have an experienced cannabis law defense lawyer on your side who can call into question any questionable evidence being used against you. This is true if you failed a marijuana breathalyzer or any other form of testing.

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