Scientists Find Basis for Reliable Marijuana Breathalyzer


Research scientists believe they are one significant step closer to developing reliable marijuana breathalyzer technology suitable for roadside intoxication tests.

The National Institute of Standards and Technology (NIST) has recently announced the results of a study on the fundamental physical properties of delta-9 tetrahydrocannabinol (THC) that could change the way law enforcement and the judicial system measure and enforce marijuana intoxication for years to come.

Published in Forensic Chemistry, the study shows how NIST researchers measured the vapor pressure of THC — something that’s proven difficult to accomplish in the past due to the relatively large size and complexity of the THC molecule.

“Vapor pressure describes how a compound behaves when it transitions from a liquid to a gas,” said Tara Lovestead, a NIST chemical engineer and the lead author of the study. “That’s what happens in your lungs when a molecule leaves the blood to be exhaled in your breath. So if you want to accurately measure blood levels based on breath, you need to know the vapor pressure.”

Traditional breath analyzers used to “estimate” blood alcohol content (BAC) from a sample breath take a precise measure of the ethyl alcohol molecule. Once alcohol has been consumed, it is absorbed into the oxygenated bloodstream via the small intestine and passes through small air sacs in the lungs where it (ethyl alcohol molecule) can be expelled with a breath and measured.

Credit: Kelly Irvine/NIST

Credit: Kelly Irvine/NIST

But unlike the large and complex THC molecule, the ethyl alcohol molecule is small and escapes into the air with ease — its high vapor pressures makes it relatively easy to measure. The THC molecule, on the other hand, has very low vapor pressure — its complex shape keeps THC molecules stuck together.

An Explosive Discovery

In 2009, researchers attempting to “sniff the air” for traces of explosives at airports developed a technology called PLOT-cyro (porous layer open tubular cryogenic adsorption). “PLOT-cryo is an extremely sensitive technique for capturing and analyzing things in the vapor phase,” said Tom Bruno, NIST research chemist and co-author of the marijuana breathalyzer study. “It was a natural candidate for this type of problem.” The technology is in use today to “sniff fire debris for evidence of arson and to find clandestine graves by following the faintest scent of decomposition.”

NIST researchers turned to the PLOT-cryo technology to measure escaping THC molecules from a pure THC sample purchased through a DEA research license. Once measured, researchers could calculate the elusive vapor pressure.

A Measurement Makes the Difference

The NIST contributes to alcohol breathalyzers by manufacturing ampules of ethyl alcohol mixed to extremely precise concentrations. Law enforcement agencies around the country use these precise mixtures as a standard reference to calibrate their breathalyzers, ensuring various equipment across jurisdictions produces consistent results. “Fundamental measurements are the basis of standardization,” Bruno said. “We’re laying the foundation for the reliable systems of the future.”

It is believed that the same process could be used to calibrate THC breathalyzers in the future.

About Author Managing Editor, I studied Literature at UC Irvine and earned my MBA at Chapman University. Eventually, I will spend my days writing fiction from a small balcony in Maastricht, Netherlands, a couple of hours south of Amsterdam. For now, I'm quite content with a life of reading, writing, and surfing in San Clemente, CA.


  1. It doesn’t mater how accurate your devise is it still will not determine impairment. The differences in the individuals response to cannabis is determined by a myriad of different causes. Tolerance is one. The amounts of usage that is normal for that individual and the differences in physiology.

    • A lot of the same things are true for alcohol, but that didn’t get in the way of per-se limits and mandatory enforcement of DUI.

      Same will happen with weed. Limits will be set, breathalyzers will be put into use, and if you are over the limit, you’ll be guilty regardless.

      Sometimes the wish to be treated like alcohol can backfire.

  2. They’re testing is based on junk science there is only two type of THC out of 12, that is phycoactive, one is THCa once heated at 156^c converts to THC that is phycoactive the second is THCV which activates at 106^c and gets destroyed at 112^c and has lost its activeness above this temperature which is what they test for, the 9 known types of delta-9, 2 known types of delta-8, and 1 delta-7.

    In addition to that, medical testing labs are not testing for THCV. They are testing for the presence of 11-Nor-9-Carboxy-THC aka 11-OH-THC/11-COOH-THC aka THC-OH/THC-COOH, a secondary metabolite of THC that is broken down by the liver when consumed. Depending on the accuracy of the testing equipment, they can further isolate 11-OH-THC and 11-COOH-THC to determine if the exposure was recent. When only 11-COOH-THC is present, the use would have been some time ago, but when both 11-OH-THC and 11-COOH-THC are present, the exposure would have been much more recent This is a great report on the entire breakdown of all the phytocannabinoids in cannabis but is not active at the time of testing.

  3. I completely agree with the other comments here.. This is completely junk science & is basically a witch hunt! Because of the way it stays in the body for a long period of time, tolerance lvls of daily users & the way it differently dissipates in every person.. This is impossible to tell wether someone used THC 5 min ago, 5hrs ago or 5 days ago!! This is blatantly nothing more than a rush to get a tool out asap so they can start ruining people’s lives & a way for law enforcement to cash in on the weed boom! Not to mention that the Marijuana/THC high really only lasts 15min to 30min tops!! And.. There will nvr be a way to distinguish between a user using 15 min ago or 10 hrs ago!
    But.. Law enforcement does not care! All they want is to determine if a person is a user, so they can bulldoze you with a DUI & peg you as a criminal drug user! Regardless of “when” or “why” a person uses cannabis!
    I have MS & the government has began to strip all chronic pain sufferers from even the smallest amount of opiate pain medication & the government does not care if you are bed ridden with pain without opiates or you’re a junkie crushing pills to smoke or injecting IV!
    In their eyes you are a criminal! My Dr’s have heard from DEA that b4 2020 there will be a law in place making it illegal for a dr to prescribe an opiate for any reason!
    Even if you’re terminally ill with 30-90 days to live.. You will not be prescribed an opiate for pain!


      As a child in the 60s I used recreational once in awhile but fast forward to 2016 was in a bad traffic accident with a commercial truck the pain medicine ( Opioids) were keeping me in the clouds with nasty side affects my doctor said there having great results with medical marijuana I went through the process and started treatment that was over seen by my Doctor I decided to start a new career in class A driving my doctor told me to stop 2 months prior to starting this should be long enough to not show on a drug screening now getting back on topic I’m a big guy 280 lbs the bigger you are the longer is shows up,after 67 days not using and being under a doctors care I showed up positive so a better test needs to be found to accurately test if your under the influence.
      Not everyone is going to test the same a girl weight 90 lbs will show up negative in a week now a guy weighs 300 lbs showed positive after 30 day both consumed the same amount.
      The government has failed us again if your under a doctors supervision you should be exempt from this test but still liable if your under the influence like others have said the high last 15-20 minutes but still impaired .
      But 3 days later it’s still in your system but buy no means are you impaired thus is the area we need to focus on and not a quick fix that is bad
      And not accurate we should be able to identify if someone smoked an hour ago or 10 days ago

  4. The whole problem is finding the .08 of weed. In other words pot smokers should be able to go to a bar and enjoy some herb and still be able to drive home like we do now when we go out for a meal and have beer and still be to drive home legally. But most people respond to one drink (beer, wine or cocktail) roughly the same depending on body weight.

    But with weed the same quantity will effect people differently depending on how many years they’ve been smoking. So I really don’t think the gizmo above takes in to account any of that and the gizmo will have a hard time standing up to a scientific explanation!

  5. There is no scientific basis for INTOXICATION of marijuana consumption because marijuana is nontoxic. Marijuana is psychoactive if it contains more THC than its counteractive cannabinoid THC.
    The only way that marijuana consumption contains even remote, non lethal toxicity is when smoked. And unless the smoke is impeding one’s visibility through the windshield like the classic image of Cheech and Chong, or other additives cause a cough attack from hitting a blunt while driving, the trace amounts of carbon monoxide and other byproducts of consumption are not enough to impede one’s clinical judgement or cause physical impairment while driving, according to data collected by the NHTSA.
    PLEASE Mr Hale… PLEASE stop refering to marijuana incorrectly as “toxic.” Big Pharma and Project SAM are grinning from ear to ear every time you call marijuana “toxic” and if you dont improve your editing even after being provided the facts we at NORML and the advocacy community will be left with no other recourse but to assume you are complicit with propaganda.

    • “Marijuana is psychoactive if it contains more THC than its counteractive cannabinoid CBD.”

      See? I can edit myself. Please do the same in regards to toxicity v. psychoactivity of marijuana. Legalization is counting on us.

  6. Jack Wilborn on

    Per Se limits with CNS depressants are a known situation. This link is to the AAA and states “Legal limits, also known as per se limits, for marijuana and driving are arbitrary and unsupported by science.”

    And the NHTSA (National Highway Traffic Safety Administration)

    “Drug per se laws are not quite analogous to the alcohol impaired-driving per se laws now in effect in every State make it illegal to operate a motor vehicle with a blood alcohol concentration (BAC) of .08 grams per deciliter or greater. Alcohol-impaired driving per se laws are based on evidence that all drivers are impaired at .08 BAC. Drug per se laws are more analogous to zero-tolerance laws that make it illegal to drive with certain drugs in the system.”

    It’s very interesting as they evaluate states with and without DRE and Per Se laws.,-18,549

    NHTSA February 2015 executive summery states…

    “Drivers testing positive for THC were overrepresented in the crash-involved (case) population. However, when demographic factors (age and gender) and alcohol use were controlled, the study did not find an increase in population-based crash risk associated with THC use.”

    Its a good read… This study pretty much tell what drug is killing people on the highways. Alcohol.


  7. Funny how we have been using weed daily for many decades, going to work, dropping the kids at school, grocery shopping ,etc with no problems and now it matters? Need to do something about drug testing for a job, bs. Anything they come up with had better be accurate. How are they going to factor in that it affects everyone differently? growing pains I guess.

  8. rob woodside on

    Some years ago when the US and the UK were trying to “pacify” Iraq, the was a helpful company who made millions by selling divining rods to locate bombs. They made millions confirming the stupidity of security types with the useless sticks. Eventually the fraud was realized and the helpful company bankrupted.
    The same situation is developing with the Reefer Madness Crew demanding road side breathalysers for dope. Unlike the divining rods these machines may actually measure THC blood content, but that has little to do with impairment Until they sort out the difference between THC in the blood and impairment, there will be a lot of falsely accused people.
    No one wants to endanger themselves or anyone else, but we’ve been driving stoned for over 50 years and there’s been no increase in traffic accidents with legal dope. So you can forget about the hysteria fomented by the Reefer Madness Crew.

  9. I agree what we do not need is more invasive government testing of our bodily fluids and loss of our privacy. If the government could get away with it, they would shove a butt plug up everyone’s asses with a meter that displays any chemicals they wish to monitor. Just tell the government to stop it.

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