There’s been a new breakthrough in the development of a marijuana breathalyzer, with a study partly funded by the Justice Department showing a potential pathway for a “portable, low cost” device that looks like an inhaler for asthma, built with 3-D printed material that can detect delta-9 THC without secondary lab analysis.
The study, led by Emanuele Alves at Virginia Commonwealth University (VCU), detailed the results of experiments meant to address the current lack of a roadside impairment test for THC similar to those utilized by law enforcement for people suspected of driving under the influence of alcohol. With more states legalizing cannabis, there’s particular “need for rapid, reliable and low-cost roadside tools,” it says.
By using 3-D printed cartridges with a “Fast Blue” dye and gelatin system, the colorimetric experiments established “foundational data” that the device can be used to detect delta-9 THC, CBD and CBN “across multiple matrix systems.”
The tool was able to detect 10-100 nanograms of the cannabinoids, which could be differentiated using color-space modeling. Specifically, the tests revealed “two primary clusters,” with evidence that delta-9 THC and CBN analytes can be distinguished from CBD analytes based on color hue.
“Overall, this project established foundational data supporting the feasibility of a portable, low-cost, colorimetric tool for detecting cannabinoids using 3D-printed cartridges and readily accessible reagents,” the study says. “While additional validation and field-oriented development are needed, these findings provide a proof-of-concept framework for future roadside or point-of-collection testing technologies.”
The Justice Department provided funding for the study and posted the results on the Office of Justice Programs’s National Criminal Justice Reference Service website last month, but the author’s findings “do not necessarily reflect the official position or policies” of the agency, it says.
“The development of a breathalyzer for the early detection of marijuana’s recent use is an important matter considering the current legal status of marijuana-based products around the country,” VCU’s Alves said. “To achieve this goal, our initial approach was to develop a portable cartridge that would be able to react with cannabinoids selectively to detect THC use, but not CBD.”
“Most THC breathalyzers in the market are merely collection devices that will need further laboratory analysis,” he continued. “Considering the working system of an alcohol breathalyzer, using a redox reaction would be risky for the THC approach as it would not be selective for the specific cannabinoids and it would give a positive result to any molecule capable of oxidizing the reagent.”
Because of the “excellent results” of the experiment in the “establishment of the foundational chemical profile needed for the development of a THC breathalyzer,” the study says, a patent application has been filed with the U.S. Patent and Trademark Office (USPTO), with a proposed design for a future prototype.
There are three main components to the device, which the author said looks similar to inhalers for people with asthma. There’s a mouthpiece for exhaled air to be collected, a cartridge fixed to the end of the instrument where delta-9 THC particles “collide and react” and a detection system where the colorimetric reaction occurs and forms a dark red color if it’s positive for the intoxicating cannabinoid.
“The consequences and legal penalties for driving under the influence (DUI) of alcohol are well publicized,” the study concludes. “However, what the general population ignores is the illegality of DUI of marijuana, in combination or not with other drugs.”
“With the legalization of cannabis consumption in many parts of the USA, this lack of information from the general population has increased the risk of accidents and deaths caused by drivers intoxicated with marijuana. Due to the difficult and costly current methods available for the detection of marijuana in samples, it is vital to create and improve technologies for its detection in a fast, reliable, and in situ method for public safety and awareness.”
“The outcome of this project is the fundamental chemical foundation and the initial prototype for the development of a ∆9-THC breathalyzer,” the author said. “The device developed in this project is a portable tool to increase safety on the roads and for ∆9-THC use monitoring.”
Federal agencies outside of DOJ have also recognized the need for the THC detection technology. For example, last year the National Institute of Standards and Technology (NIST) under the U.S. Department of Commerce planned a workshop aimed at facilitating “an open and candid discussion” about the development and implementation of device to test a person’s breath for marijuana impairment.
In 2023, a federally funded report by researchers at NIST and the University of Colorado Boulder concluded that evidence does “not support the idea that detecting THC in breath as a single measurement could reliably indicate recent cannabis use.”
A DOJ researcher in 2024, meanwhile, cast doubt on whether a person’s THC levels are even a reliable indicator of impairment, saying states may need to “get away from that idea.”
Scott questioned the efficacy of setting “per se” THC limits for driving that some states have enacted, making it so a person can be charged with driving while impaired based on the concentration of cannabis components in their system. Ultimately, there may not be a way to assess impairment from THC like we do for alcohol, she said.
One complication is that “if you have chronic users versus infrequent users, they have very different concentrations correlated to different effects,” Scott said. “So the same effect level, if you will, will be correlated with a very different concentration of THC in the blood of a chronic user versus an infrequent user.”
That issue was also examined in a federally funded study in 2024 that identified two different methods of more accurately testing for recent THC use that accounts for the fact that metabolites of the cannabinoid can stay present in a person’s system for weeks or months after consumption.
Also that year, researchers behind a federally funded study said they’d developed new procedures to enhance the selectivity of a popular forensic testing method, allowing better detection of delta-9 THC and its metabolites in blood.
A 2023 congressional report for a Transportation, Housing and Urban Development, and Related Agencies (THUD) bill said that the House Appropriations Committee “continues to support the development of an objective standard to measure marijuana impairment and a related field sobriety test to ensure highway safety.”
A study published in 2019 concluded that those who drive at the legal THC limit—which is typically between two to five nanograms of THC per milliliter of blood—were not statistically more likely to be involved in an accident compared to people who haven’t used marijuana.
Separately, the Congressional Research Service (CRS) in 2019 determined that while “marijuana consumption can affect a person’s response times and motor performance … studies of the impact of marijuana consumption on a driver’s risk of being involved in a crash have produced conflicting results, with some studies finding little or no increased risk of a crash from marijuana usage.”
Another study from 2022 found that smoking CBD-rich marijuana had “no significant impact” on driving ability, despite the fact that all study participants exceeded the per se limit for THC in their blood.
In a separate report last year, the U.S. National Highway Traffic Safety Administration (NHTSA) said there’s “relatively little research” backing the idea that THC concentration in the blood can be used to determine impairment, again calling into question laws in several states that set “per se” limits for cannabinoid metabolites.
“Several states have determined legal per se definitions of cannabis impairment, but relatively little research supports their relationship to crash risk,” that report said. “Unlike the research consensus that establishes a clear correlation between [blood alcohol content] and crash risk, drug concentration in blood does not correlate to driving impairment.”
Congressional lawmakers at hearings last year also heard from representatives of the trucking industry, who called for wider use of hair-follicle testing in the industry. The chair of the National Transportation Safety Board (NTSB), meanwhile, recommended better education for drivers.
“At time when conversations lean towards the potential reclassification of marijuana from a Schedule I to Schedule III narcotic, demonstrating that this problem is likely to only grow,” said a representative for Truckload Carriers Association, “our industry in its entirety is unable to properly employ the proper test to identify habitual users and enter them into a substance abuse program and begin the return-of-duty procedures.”
The transportation industry also advised Congress in January that if marijuana is federally rescheduled, businesses want assurances that they won’t have to forgo zero-tolerance drug policies for drivers—while stressing that a key problem for the sector is a lack of technology to detect impaired driving.
The issue of marijuana-impaired driving also arose at another recent congressional hearing, with a representative of the Governors Highway Safety Association emphasizing the importance of roadside drug testing as a tool to help combat deadly car crashes.
Last year, meanwhile, the U.S. Supreme Court ruled in favor of a trucker who sued a cannabis company after he was fired over a positive THC test that he said was caused by consuming a hemp-derived CBD product.
Separately, a Substance Abuse and Mental Health Services Administration (SAMHSA) official recently downplayed criticism from the CEO of a drug-testing company that more widespread use of saliva-based drug testing “means truckers who use cannabis will be able to do so with near impunity, as long as they avoid a drug test for a couple of days.”
“When a donor receives a request for collection, the donor will not know if the test will be an oral fluid or urine collection until they arrive at the collection facility for a federal agency,” the unidentified SAMHSA official said in response. Not knowing whether to expect a saliva or urine test, in other words, would prevent drivers simply stopping marijuana use a few days before a saliva-based test.
