What Are Cannabis Breathalyzers and What Do They Check?

Everything you need to know


With marijuana now legal for medicinal purposes in a majority of American states, and completely legal in Canada, law enforcement has a new problem: An increased number of stoned motorists. Whether we like to admit it or not, driving while high is NOT a good idea. As a result, companies are doing their best to create a cannabis breathalyzer which can detect THC, the most prevalent psychoactive compound, in a person’s blood.

In theory, a police officer will be able to stop someone suspected of driving while high and administer a test similar to what is available to test potentially drunk drivers. It is a technological advance that proved elusive – until now that is.

Are We About to See the World’s First Marijuana Breathalyzer?

The California Highway Patrol (CHP) already uses a marijuana test of sorts; a plastic swab stick stuck into a computerized unit that looks a bit like a portable credit card reader. It was developed by Alere Toxicology, and a representative for the company claims the device has a 95% accuracy rate. It tests for weed, opiates, methamphetamines, and cocaine.

The device tests a person’s saliva and can detect whether you have used weed within a couple of hours by testing the saliva for THC-COOH, also known as THC metabolites. It is a necessary step, although we find it odd that California doesn’t have a cannabis intoxication threshold; there is one in Washington of 5 nanograms per ml of blood, and it is even stricter in Nevada at 2ng/ml.

A New Form of Marijuana Testing

It seems as if Hound Labs, a diagnostics company based in Oakland, is about to go one step further and introduce a functional marijuana breathalyzer to the market. If it works, it will propel the company to fame and help law enforcement catch and arrest stoned drivers. Hound Labs first began working on the device back in 2015, and at the time of writing, it is not yet available commercially.

The company first began conducting clinical trials in 2016 and the following year at TechCrunch, Hound Labs’ founder, Mike Lynn, was asked “Why are you such a narc?” onstage! In recent times, Lynn said “we’re not Theranos,” a thinly veiled swipe at the company infamous for crappy blood testing technology.

Hound Labs claims to have conducted a vast array of testing although some of these tests have rightly been criticized. One of the daftest had to be a video, uploaded to YouTube, which shows high drivers crashing into things. Hound invited the volunteers to get as high as they wanted then drive at 65 miles an hour around a 1.5-mile track. In this situation, there was a 99% chance of the motorists hitting objects, yet Hound laughably claimed it was the equivalent of hitting cyclists on the road.

The device consists of a small plastic cartridge that slides into a device which resembles a cellphone from the late 1980s. A small plastic tube sticks out at one end, and you are supposed to blow into it for 30 seconds. On the screen, you can see indicator bars which detect THC in your breath.

According to the company, the device will detect whether you have consumed weed within the last two hours. To be fair, it makes sense to minimize the timeframe to prevent individuals from being arrested because they had a joint the night before. There is also a base station which is around the same size as a standard laptop. Its main role is to protect the cartridge which can be damaged by extreme cold or hot temperatures.

Interestingly, the Hound Labs device also acts as a standard alcohol breathalyzer which gives law enforcement officials a handy two-in-one testing kit.

The Problem with Marijuana Testing

At present, it is next to impossible for police officers to scientifically test for marijuana use roadside. Yes, they can assume consumption based on a driver’s appearance or behavior and can smell weed from the car. When it comes to alcohol consumption, there are per se drunk driving laws which mean drivers are automatically guilty of DUI if their Blood Alcohol Concentration (BAC) level is at 0.08 or greater.

In Canada, provincial and federal governments have introduced per se laws with regards to marijuana. If you are caught driving with a blood THC level of 5ng/ml or greater, it is classified as a federal crime, which means up to 10 years in prison if found guilty! Canadian provinces are allowed to be even stricter, and in Quebec, a ‘zero tolerance’ policy is being considered.

The problem with marijuana per se laws is that they are not based on good science. Several American states also say that you are guilty of DUI if the THC level in your blood is 5ng/ml or over. These limits are completely arbitrary and come as a result of treating weed and alcohol as the same kind of drug, even though they are completely different.

First and foremost, alcohol is water-soluble, which means it diffuses through the body quickly. Its peak effects and impairment tend to occur up to an hour after ingestion, and it slowly reduces over time. Therefore, alcohol breathalyzers can provide police officers with a solid measurement of driver impairment.

Marijuana behaves differently in the body. First of all, THC is not particularly soluble in blood, so it gets taken in by our fat stores. Our maximum THC level occurs within 10 minutes of smoking, and in some tests, it was shown that blood levels fall below 5 ug/L after 84 minutes, and below 2.0 after 198 minutes, although some people stayed above 2 ug/L for up to 8 hours.

As THC builds up in our fat cells, it gets released over a long time so you could have it in your blood from previous exposure. In other words, it is possible to ‘fail’ an impairment test even though you haven’t used weed that day. Furthermore, it is effectively impossible to link a blood THC measurement to impairment levels because it can easily cause impairment in an individual with a reading of 2ng/ml.

In Canada, a female driver, who is a medical marijuana patient, temporarily lost her license because a roadside oral fluid test showed she was above the legal limit. Even though she passed a DRE examination at the police station, she lost her license for a week and had to pay $150. Her car was also impounded, and she had to pay $250 to get it back.

To What Degree Does Marijuana Impair Driving Performance?

That is the million-dollar question, and until it is answered, there is no evidence that Hound Labs’ device will even be effective. The existing tests on the market test for saliva, urine, or blood, and it can take days for the test results to arrive. These tests also can’t tell if a person used weed a week ago or an hour ago.

Hound Labs claims that it has navigated the scientific and technical hurdles, and can accurately measure THC in a person’s breath molecules in parts per trillion; that’s a bold claim. Yet it is necessary for any marijuana breathalyzer to be this accurate. While impairment from alcohol is measured in parts per thousand, THC has a concentration of up to one billion times less.

According to Lynn, this technical issue is the main reason why Hound Labs has taken five years to perfect the device. While the machine can detect THC in your breath, it is unable to calculate how much THC you have consumed. Several police departments should be testing the breathalyzer as we speak in the hope it can provide them with the objective roadside data that has previously eluded them.

However, is this device likely to be effective since there is a lack of evidence to link THC with traffic accidents caused by impaired driving? A study by Keyes, Brady, and Li, published in Injury Epidemiology in 2015, showed that approximately half of young drivers (aged 16-25) who were involved in a fatal traffic accident were under the influence of weed, alcohol, or both.

Researchers acknowledge that they don’t know the extent to which cannabis affects a driver’s judgment, skill, or response. A 2015 study by the United States Department of Transportation looked at the impact of weed on driving. It found that once adjustments for gender, age, race, and alcohol use were taken into account, drivers who tested positive for weed were no more likely to cause a crash than drivers who didn’t use alcohol or drugs before driving.

It also seems as if marijuana impacts drivers differently than alcohol. According to one Harvard researcher, drunk drivers run red lights while stoned drivers stop at green lights! Of course, this kind of driving can also cause accidents.

A Dubious Breakthrough

In late February 2019, Hound Labs proudly announced the results of its second clinical trial involving the Hound Breathalyzer. It was conducted at the University of California San Francisco (UCSF) and featured 20 volunteers. The device measured their breath over a three-hour period and took nine samples from each person. According to Dr. Kara Lynch of the UCSF, it was the largest study of its kind to date.

According to the researchers, the trial found that THC moves quickly from the blood to the breath and appears in very low concentrations for up to three hours. They also said it was proof that the technology is ultra-sensitive and capable of measuring THC in a person’s breath in parts for trillion, also known as picograms.

Hound said it validated their claims which is an odd statement to make since no one outside of the UCSF researchers and the 20 volunteers have tested the device. Last time we checked; new drugs are not approved on the strength of one tiny clinical study. The volunteers brought their own weed and consumed it.

Lynn also made a rather troubling statement. He admitted that the breathalyzer would show THC in your breath if you used any in the previous two hours. In other words, you will ‘fail’ the test whether you have half a dozen bong hits or a small puff of a joint. You could theoretically get arrested and lose your job for taking a small bite of an edible at lunchtime in a state where it is perfectly legal to do so.

Remember, we are just about coming to terms with the fact that cannabis microdosing could have health benefits. One would hope that the Hound device does fulfil its promise to ensure your ng/ml reading is accurate. Otherwise, there will be a spike in the number of DUI arrests. This is great news for any officers seeking to fulfil their monthly quota, not so good for legal marijuana users who microdose.

Final Thoughts on the Marijuana Breathalyzer

At present, we simply don’t know the extent to which marijuana consumption impacts a person’s driving skills. Logically, it stands to reason that it impairs you, but we don’t know the degree. Studies to date show that drivers under the influence of cannabis are less likely to be reckless drivers but travelling too slowly or failing to indicate when turning can cause an accident just like overtaking in the wrong place or driving too fast can.

A marijuana breathalyzer works well in theory. This is especially the case if Hound Labs’ device IS genuinely capable of determining the level of THC in the blood. The main problem is that no state or nation has a clue what the ‘correct’ impairment level should be. The existing limits are utterly useless because they wrongly treat cannabis and alcohol as similar drugs.

There is no question that law enforcement needs assistance on this issue because increased legalization means there are more people who use pot and drive than ever before. We simply can’t allow drivers to get stoned before hitting the highway. However, there seem to be a few flaws in the mooted marijuana breathalyzer, and after years of testing, we still don’t know if and when Hound Labs will officially launch its device.