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Researchers Are One Step Closer to a THC Breathalyzer

July 25, 2017
Federal researchers at a Colorado lab of the National Institute of Standards and Technology (NIST) have figured out how to measure the vapor pressure of THC, one of the main psychoactive chemicals in cannabis. The discovery means law enforcement officers could someday test for cannabis impairment based on a person’s breath.

The key: Breath sampling may show very recent use, not latent metabolytes.

The traditional tests for cannabis use — blood draws and urine samples — do an adequate job of detecting the past THC usage. But they aren’t very good at figuring out whether someone is currently impaired by THC. Some states, like Washington, allow police officers to test drivers for a cannabis-related DUI by drawing their blood. But traces of THC can stay in the bloodstream of regular consumers for up to seven days, according to the National Organization for the Reform of Marijuana Laws.

Employers have run into a similar dilemma. Out of fear of workplace accidents, rejected insurance claims and lawsuits, many businesses in legal states continue to screen their employees for marijuana use. But testing positive for THC isn’t the same as being impaired; conflating the two raises privacy questions. So long as nurses and forklift operators shows up to work sober, should their employers have a say over what they do in their free time?


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‘The Quest’ Continues

These findings, published in the latest issue of Forensic Chemistry, come from the National Institute of Standards and Technology, a branch of the Department of Commerce.

“The quest for a reliable means to detect cannabis intoxication with a breathalyzer is ongoing,” the researchers, Tara Lovestead and Thomas Bruno, wrote. “Breath sampling is attractive because it is non-invasive, can be portable, and has been shown to indicate recent use within [thirty minutes to two hours].”

When asked why they decided to study THC molecules, Lovestead told Leafly, “Well, I’m in Colorado.” She’s been working on this project for about three years. The idea was initially inspired by the state’s legalization of marijuana use, in 2012. After getting approval from the DEA — a process that took about nine months — Lovestead got to work.


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You Measure the Vapor Pressure of THC

To explain the science, she gave the example of a closed, partially finished liquor bottle. Some of the ethanol is in liquid form. There’s also gaseous ethanol molecules trapped in the enclosed air space above.

If you know how much pressure is produced by ethanol vapor, you can figure out how much ethanol is left in the bottle based on properties of those gases. The same logic applies for THC leaving a human body in exhaled breath. This chemistry can be used to create an ethanol breathalyzer. But scientists have previously struggled to figure out the vapor pressure of THC, which is a relatively complex molecule.

For those without much of a chemistry background, this can be confusing science. But it has a stunning range of applications. In the past, Lovestead has investigated food spoilage by examining the vapors above rotting chicken. She’s also studied the gases left over after a fire —the composition of which can help law-enforcement determine if a blaze resulted from arson.


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Lovestead thinks it will still be a while before cops and employers have a real, working cannabis breathalyzer.

“THC alone is probably not a good marker” of cannabis intoxication, she said, citing a number of other chemicals, including CBD, which she suggested might also need to be measured. She also points out that cops will need more than just a measurement itself; they’ll need to figure out the how those numbers relate to real-world impairment. She thinks other methods, like field sobriety tests, will help fill in that picture.

Still, scientists have cracked at least one of the puzzles necessary to build a cannabis breathalyzer. The time range — vapor readings can show THC ingestion within the last 30 minutes to two hours, according to the paper — makes it a far more practical tool for situations like possible cannabis DUIs. But this government push to create a better device for testing cannabis impairment suffers from one ironic setback. The Drug Enforcement Agency continues to treat cannabis as a Schedule I drug. Although Lovestead could walk into a dispensary anywhere in Colorado and legally a joint, as a federal researcher, it was tricky for her to get the permissions necessary to study cannabis.


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NIDA Seeks a DUI App

Meanwhile, in Washington DC, the National Institute on Drug Abuse (NIDA) is hoping to find a way to measure marijuana-related impairment without relying on exhaled breath. In late June, the agency published a request for proposals related to “digital markers for marijuana intoxication.” In other words, they’re hoping somebody will invent an iPhone app that law enforcement can use to determine possible cannabis-related impairment.

From the RFP:

The app features may leverage and integrate with the internal sensors, compatible adapters and external hardware to monitor the measurable markers of marijuana intoxication. Examples of the app features may include, but not limited to, accelerometer, microphone, gyroscope, facial or eye pupil’s changes recognition software, glucometers, inhalers, skin voltage sensor, heart rate sensor, other existing and newly developed sensors.

More details about the RFP can be found here. NIDA plans to fund as many as three to four projects for $225,000 to $1.5 million.

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Stephen Paulsen

Stephen Paulsen is a freelance journalist based in Houston. He writes about crime, food, drugs, subcultures, and urban planning.

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  • 360dunk

    It makes total sense to test a driver who’s been smoking pot within the last couple of hours. That way, the police won’t be able to ticket a motorist for something he or she smoked three weeks ago at a party. Obviously that person is not intoxicated from cannabis after two or three weeks, even if it DOES show up in their system.

    • rhadak

      So how would they determine from a test when the pot was ingested? Moreover, nowhere in the article was evidence produced that pot impairs driving. This whole testing regime is premised on the notion that pot impairs driving. It’s a false premise. This is nothing more than another effort to enrich the drug testing industry.

  • Steve Mc Laughlin

    This type of testing, when available, will mean no more random testing. Just like with alcohol now show up for work questionable, test on the spot. Otherwise what You do on Your own time can no longer be used to persecute.

  • nedhoey

    There is a fallacy at work here. While authorities are quite satisfied they have alcohol testing nailed down, it remains imperfect. It just works in court for them and that is good enough as far as they’re concerned. Impairment threshold on anything is variable for different people and the best test of that is in the moment with performance tests that are also video recorded, so it isn’t just the cop’s on the spot assessment. For experienced regular users of cannabis, it’s debatable whether they are ever truly legally impaired. They have been driving for decades while using with no recognizable or statistical increase in accidents. All these years of Prohibition they were out there, driving around, living their lives. But non users simply can’t accept that. If it makes you “high”, you must be impaired! they say. So we must go through this elaborate theater to find a legal standard and method. What they do may have some validity with occasional and inexperienced users. Those folks can get a bit effected by taking one hit too many but it won’t apply fairly to all users.

    • Greg Brennum

      You contradict yourself. Without testing, how do you know the statistical numbers of accidents involving people under the influence of marijuana?

      • rhadak

        You’re putting the cart before the horse. Before the state begins to test drivers for THC impairment, they should first demonstrate that THC impairs driving. There is no statistical evidence that THC impairs driving. In fact, due to many studies, someone with THC present in their system have no more accidents than those who have none. In most cases of accidents when drivers were under the influence it was a combination of THC and alcohol.

        “Today, a large body of research exists exploring the impact of marijuana on psychomotor skills and actual driving performance. This research consists of driving simulator studies, on-road performance studies, crash culpability studies, and summary reviews of the existing evidence. To date, the result of this research is fairly consistent: Marijuana has a measurable yet relatively mild effect on psychomotor skills, yet it does not appear to play a significant role in vehicle crashes, particularly when compared to alcohol. Below is a summary of some of the existing data.”

        “Epidemiological studies have been inconclusive regarding whether cannabis use causes an increased risk of accidents; in contrast, unanimity exists that alcohol use increases crash risk.”

        “The study also found, after adjusting for demographic factors like age, gender and race, as well as alcohol use, marijuana users were not at a greater risk to crash than sober drivers.”

      • nedhoey

        Not at all. Having spent 40 + years immersed in California’s cannabis subculture, I have broad extensive (if technically anecdotal) firsthand experience of this. If the problem was statistically significant at all, it would have revealed itself long ago. The roads of the heavy pot growing counties have been regularly traveled FOR DECADES by heavy users. I’m not aware of any “crisis” or even any notable attribution of accidents in those places to “stoned” driving. The effects of alcohol and THC are profoundly different and in no meaningful way can they be conflated. You’ve missed the point, no test as described here can determine genuine impairment. Detecting amounts tells you very little in that regard.

  • Christopher Pratt

    Great…another test I have to learn to pass. The damn driving test was hard enuf!

    • Roger A Weaver

      I think everyone should see things the way that I see them. Tech is good. I would install every vehicle with a BREATHALYZER that registers Alcohol & THC levels, that the driver must use in order to start the vehicle, if over limit car will not start. A drunk driver killed my youngest daughter. Do not operate any machinery if you over use any substance. LIFE is on the line! Does not hurt anyone who is within reasonable levels!