Cannabis Science

What is the Marijuana Breathalyzer Test?

picture of a man driving

There are many ways to detect cannabis in the body. There are urine tests, blood tests and saliva tests. There is even a way to find out if you’ve been exposed to cannabis from your hair. Even though there are over one hundred cannabinoids found in cannabis, these tests focus on one cannabinoid only. Usually, people are interested in knowing whether or not you’ve got tetrahydrocannabinol (THC), the main psychoactive cannabinoid found in cannabis. 

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Even though there are many tests for THC, there were none that were instant. You’ve probably heard of a breathalyzer to detect alcohol on the spot but did you know that a marijuana breathalyzer was developed? 

According to Science Daily, there was concern about enforcing DUI (Driving Under the Influence) laws since there was no similar technology available to serve as a breathalyzer for marijuana. This concern comes on the heels of marijuana legalization in many states. 

A team of researchers at the Department of Chemistry and the Swanson School of Engineering developed a breathalyzer that can detect THC in someone’s breath. Here’s the science behind it.

The science behind the breathalyzer test 

The team used carbon nanotubes, which according to Science Daily are tiny tubes of carbon 100,000 times smaller than a human hair. The technology being used is nanotechnology. The nanotechnology sensors are said to be even better than mass spectrometry which is regarded as the gold standard. 

When a person breathes into the tube, if the THC molecule is present, it will bind to the surface of the nanotubes. That will prompt a change in their electrical properties. The speed at which the electrical currents recover will then signal whether THC is present or not. Sean Hwang, lead author on the paper and a doctoral candidate in chemistry at Pitt was quoted on Science Daily saying, “We used machine learning to ‘teach’ the breathalyzer to recognize the presence of THC based on the electrical currents recovery time, even when there are other substances, like alcohol, present in the breath.”

The prototype they have is similar to the one made for detecting alcohol. It has a plastic casing, a mouthpiece that protrudes and digital display.

Houndlabs reported that THC can be detected from the breath for 2-3 hours after smoking. They said the detection window is slightly longer if the marijuana was ingested. 

Other breathalyzers developed 

CNN mentioned another breathalyzer that was being developed by Houndlabs. This one uses mass spectrometry and will be able to detect small particles of THC to determine if someone has used marijuana in the last 2-3 hours. According to CNN, the Hound device requires the person being tested to blow into it for two minutes. The cartridge that is subsequently read in a separate bay behaves like a mass spectrometer. If THC is indeed found then “warning” will pop up on the screen. 

Hound Labs founder Mike Lynn, an emergency room doctor, reserve deputy sheriff and venture capitalist was quoted on CNN saying, “We aren’t measuring impairment, we’re measuring THC in breath where it lasts a very short period of time, providing objective data about THC in breath to law enforcement and employers to use in conjunction with other information they have gathered,”

What the critics say 

According to a CNN article published this year, in regards to the breathalyzer used for alcohol, “No such technology yet exists for cannabis, but several tech startups and university scientists say they’re close to commercializing something resembling a cannabis breathalyzer.” The article outlines issues with making a breathalyzer. For example, the critics ask whether the breathalyzer is able to detect recent cannabis use as well as prove that the amount detected can cause impairment. They are not satisfied that any of the breathalyzers made can do that. The article brings up the great point that marijuana can stay in your body for an extended period of time even after the high has worn off.

Nick Morrow, a retired narcotics investigator who now serves as an expert witness in areas such as drug symptomology and field sobriety testing was quoted in CNN saying, “We’re applying the alcohol rules to a substance that doesn’t play by them.”

Morrow is saying that simply having THC in your blood doesn’t mean it impairs you the same way having a specific amount of alcohol in your body might. According to Houndlabs, “while THC or its metabolites may remain in a person’s system for days or weeks, a person is clearly not impaired for that period of time. Only the detection window for breath corresponds closely to the peak impairment window of when someone is under the influence of marijuana”.

Some states, according to CNN, have imposed limits that make it illegal to have a specific concentration of THC in their system while driving. These are known as ‘per se’ laws. However, can being ‘high’ really impair your ability to operate a car?

Can THC make driving dangerous?

While the CNN article admits that there isn’t a lot of research done on cannabis use and driving, the National Council on Drug Abuse says there are studies that show cannabis negatively affects one’s ability to drive. According to the National Council on Drug Abuse, marijuana usage can impact your reaction time as well as your impair your judgment and coordination. 

A Congressional Service Report titled ‘Marijuana Use and Highway Safety’, admits that laboratory results have shown that using cannabis can affect a person’s response times and motor performance. However, in real life, marijuana hasn’t shown to increase the risk of an accident significantly. According to the report, “Levels of impairment that can be identified in laboratory settings may not have a significant impact in real-world settings, where many variables affect the likelihood of a crash occurring”. The report continues to say, “some researchers, and the National Highway Traffic Safety Administration, have observed that using a measure of THC as evidence of a driver’s impairment is not supported by scientific evidence to date.”

However, according to a 2013 study published in Clinical Chemistry, marijuana does impair drivers. The study says, “Evidence suggests recent smoking and/or blood THC concentrations 2–5 ng/mL are associated with substantial driving impairment, particularly in occasional smokers.”


It seems as if the breathalyzers are only able to detect THC in the breath but don’t paint the full picture to show whether or not someone is impaired. In that case, it doesn’t seem to make sense to use it for DUIs unless scientists can come up with a particular concentration of THC that reliably corresponds with impairment like what they’ve done for alcohol. As it stands, THC concentration doesn’t operate like alcohol concentration. The researchers also seem to be conflicted on whether or not THC impairs motorists and leads to accidents. It’s clear that more research is needed between driving and cannabis use.


About Trevann

Trevann is Stoner Rotation’s Jamaica-based lead writer for the Science section of our cannabis blog. She graduated with honors receiving her Bachelor of Science degree in Molecular Biology from the University of West Indies, Mona. For the last three years, she has covered some of the biggest questions around cannabis and health underpinned with research from supporting studies, medical journals and scholarly articles. Got something on your mind? You can reach her at [email protected].