Most researchers say “no”
The reality of a reliable cannabis breathalyzer varies depending on who you ask. The technology has long been promised by a handful of companies, and according to several of them, they have already delivered. But for other researchers, the answer remains just as unclear as it was 10 years ago because measuring intoxication from THC is simply much, much harder than alcohol.
Developing a reliable method for measuring the effects of cannabis on drivers can be seen as a public safety issue. For many of the 24 states that still do not allow adult-use cannabis, concerns about intoxicated driving are a wedge used by prohibitionists to keep people on the fence about cannabis reform.
And though cannabis clearly does not affect motor function in the same way as alcohol, the industry can’t waive off concerns about intoxicated driving as merely uneducated fear-mongering. In states with legal cannabis, reports vary from 9% to 32% of fatal crashes involving drivers with THC in their system — but that in no way means that the driver was currently under the influence of cannabis.
Participants in NIST studies use a cannabis breathalyzer that looks like this. Credit: J. Berry/NIST.
Compare those numbers to alcohol, which is much easier to measure and has decades of research related to drunken driving. According to the National Highway Transportation Safety Administration, drivers with at least 12.5% of the legal limit of alcohol in their system account for 25% of all fatal car accidents.
When it comes to cannabis, we simply don’t know how dangerous stoned drivers are or even how many of them are causing accidents — and that’s a huge problem.
What’s the Holdup?
Police have been using breathalyzers since 1931, shortly after Indiana University biochemist Rolla Neil Harger developed the questionably named “Drunkometer,” which was essentially a balloon containing a chemical solution that, when inflated by an inebriated person, would darken in color indicating how much alcohol that person had to drink.
The remarkably simple device worked because detecting alcohol is remarkably simple.
Unlike cannabis, when people drink alcohol, you can smell it. Intoxicated people exhale about 1 million times more ethanol in a single breath than they would in a dozen breaths after consuming cannabis, according to a study published by the National Institute of Standards and Technology.
By comparison, detecting cannabis intoxication (for lack of a better word) by a person’s breath is incredibly difficult because only a sparse amount of tiny aerosol particles containing THC are released when people exhale. A positive result doesn’t indicate if a person smoked an hour ago or earlier that month.
Continuous Conflict
To be fair, science has already delivered a litany of tests that can reliably show if a person has THC in their system through urinary analysis, saliva swabs and, yes, breathalyzers. But according to research published in the Journal of Breath Research in May 2023, “Our results do not support the idea that detecting THC in breath as a single measurement could reliably indicate recent cannabis use.”
A year later, Hound Labs, the company that manufactures the Hound Cannabis Breathalyzer, published a white paper stating that its breathalyzer could accurately detect cannabis use within an hour of smoking, 100% of the time. In addition to determining if the user was intoxicated, the white paper also claimed the breathalyzer would not yield a positive result for anyone after six hours.
Both the Hound Labs white paper and the Journal of Breath Research article used liquid chromatography tandem mass spectrometry (LC-MS/MS) in their tests and yet found completely opposing results.
The white paper and research article are only the most recent examples of conflicting results from breathalyzer manufacturers and the scientific community. The argument about the reliability of cannabis breathalyzers dates back to the launch of adult-use cannabis programs with very little headway on either side.
Conflicting research aside, the more important question is whether or not law enforcement is adopting the technology, and the short answer is: no, they are not.
Pessimism from Police
Perhaps the most damning evidence against cannabis breathalyzers is the zero-adoption rate from law enforcement. Police departments across the country have been pilot testing these breathalyzers for years, but there is no consensus on if they work. In lieu of the breathalyzer, police have relied largely on roadside sobriety tests where officers watch for slurred speech, red eyes and other signs of cannabis use such as decreased coordination and slowed reactions.
Some police departments use officers with special training, referred to as “drug recognition experts,” or DREs, to spot drug impairment. However, some courts will not accept evidence gathered by DREs because they are not medical professionals. Mouth swab tests, which check for a variety of drugs including cannabis, have been adopted by some police departments in Indiana, however false positives are a major concern and have kept most police departments from using saliva swabs to detect cannabis intoxication.
Waiting to Exhale
Scientists continue to search for the elusive cannabis breathalyzer. According to researchers at the University of California San Francisco, THC levels in a person’s breath fall by about 95% after the first three hours of use, which suggests that two cannabis breathalyzer tests, spaced about 20-30 minutes apart, could provide proof of recent use.
A two-breath study by the National Institute of Standards and Technology and University of Colorado Boulder is currently under way. The study will include approximately 45 individuals between the ages of 25-50 separated into two groups, one to test for flower consumption and the other to test for concentrate consumption. Participants will consume and then participate in 10 breath tests at different time intervals to give researchers an ideal timing between tests.
Analyzing the results of the study is expected to take several years.