What to Expect (and Not Expect) from the THC Breathalyzer

The promise of a marijuana breathalyzer has been widely mentioned in the news, with articles suggesting that this could be the reliable roadside test that officers need. Even proponents of marijuana legalization have expressed enthusiasm over such a product, explaining that a fair test for intoxication would make people less opposed to legalizing marijuana. Typing “THC breathalyzer” into Google results in the auto-complete of “THC breathalyzer stock.” All the players of marijuana legalization seem to be interested: the proponents, the watchdogs, and the investors. The promise of an accurate, non-invasive test for marijuana intoxication is attractive, but a THC breathalyzer may not be the product that delivers.

The product in the spotlight is the THC Breathalyzer by Cannabix Technologies, Inc. Cannabix’s description of the THC Breathalyzer states that its device “would be used to provide detection of THC at the roadside to identify drivers intoxicated by the use of marijuana.” The THC Breathalyzer is still in development, but data on THC breath testing can predict how Cannabix’s device will function. Such data has suggested that the THC Breathalyzer would be able to discover drivers who have recently smoked. However, it would still not be able to discern when someone has used enough to be considered an unsafe driver.

An experiment conducted in 2013 tested the breath of regular and occasional marijuana smokers to determine the length of time that THC could be detected. Taking into account both types of users, the study found that THC is only detectable between thirty minutes and two hours after smoking. (Regular smokers were those who smoked four times or more in a week, and occasional smokers were those who smoked less than two times a week.)

These results suggest that the THC Breathalyzer could limit positive results to those who have recently smoked. This offers an alternative to blood testing, where residual THC can still show up days after smoking. However, using marijuana and driving is only a problem when there is a dangerous level of impairment. Having a few sips of wine before driving away from a restaurant is generally not a safety issue. Likewise, a person can smoke a small amount of marijuana before driving and it may not have a significant effect on their driving skills.

The testing device used in the study went beyond a simple positive or negative indication, and could determine a subject’s exact breath THC concentration. While not much is known about Cannabix’s THC Breathalyzer, it may have the same ability. By being able to measure a subject’s THC breath concentration, the breathalyzer has the potential to allow police to separate dangerously intoxicated drivers from those who only have a negligible amount of THC in their system.

However, in order for this to occur, there must be evidence of the relationship between THC breath concentrations and accident risk. At this point, there isn’t any, and the largest US study on THC and crash risk found that there is no increased crash risk for drivers testing positive for THC. Without establishing a correlation between THC breath concentration and accident risk, a THC breath test lacks the ability to independently determine who is a dangerous driver.

Even if we assume that drivers with a certain THC breath concentration are dangerous, this can result in the unfair targeting of regular smokers. Despite abstaining for at least sixteen to twenty hours before testing and smoking the same amount of marijuana, the breath test experiment found that regular smokers had double the amount of THC in their breath compared to occasional smokers. Because of the lengthy period of abstinence, there could not have been any lingering intoxication from prior use, and the increase in THC levels for regular users does not reflect a greater level of intoxication.

Furthermore, while the occasional smokers had no THC found in their breath after an hour, it took two hours for the regular smokers to show no signs of THC in their breath. Essentially, regular smokers had twice the amount of THC in their breath, and it took twice the amount of time for the THC to dissipate. Since the dosage was the same between the occasional and regular smokers, it is likely the level of intoxication was at least similar. However, without knowing the dosage and time of use, sole reliance on the breath test would lead one to believe that the regular users smoked a larger amount, smoked more recently, and were more intoxicated as a result. Over-reliance on breath tests would unfairly target smokers for their amount of use, even when it may have no connection to their level of intoxication while driving. This is especially a concern for patients who have a legitimate medical need for consistent and regular marijuana use.

Even moving on from the shortcomings of a breath test, Cannabix’s product will face a major problem in being as useful and widely adopted as an alcohol breathalyzer. Every state has a statutory .08% blood alcohol concentration limit (BAC). As long as a breathalyzer gives the result of .08% or higher, the police are free to arrest drivers, and the district attorney’s office will be able to prove that they broke the law of driving with a BAC .08% or above. Herein lies the main problem with comparing the THC Breathalyzer to alcohol breathalyzers: there are no laws limiting a certain level of THC breath concentration while driving. So far, states have only used blood THC concentration as their metric. Each state must enact a THC driving limit based on breath concentration, or modify their current law to include THC breath concentration. Otherwise, the THC Breathalyzer will only be a tool for discovering drivers who have recently smoked – nothing more.

This does not mean Cannabix’s product will be useless; it just wont be the next alcohol breathalyzer. The THC Breathalyzer could be used as a companion to other forms of investigation. Police can use it to see if a driver has recently smoked marijuana, and then commence with other tests and observations to figure out the extent of the driver’s intoxication. It will be one of many tools to discover stoned drivers, but with some unique benefits. It will be less invasive than a blood test, easier to use, and it will still have the objectiveness that comes with a chemical test. Furthermore, the short detection window makes it a better candidate for determining recent use than a blood test.

Although Cannabix’s THC Breathalyzer will have a role to play in the changing landscape of marijuana use and enforcement, it will fail to match the utility of alcohol breathalyzers. THC breath tests cannot determine a subject’s accident risk and do not have the same statutory support. If Cannabix and their investors are relying on the THC Breathalyzer to take on the same role as alcohol breathalyzers, they may be quickly disillusioned. On top of positioning and selling their product, they’ll need to deal with legislatures in every state, a task that most would consider a nightmare.


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