Study Finds Breathalyzers Remain Unreliable As Pot Use Test

Consistently detecting THC in the breath of someone who has recently smoked marijuana is still not possible, according to a new study by the National Institute of Standards and Technology, and a "lot more research is needed" before a cannabis breathalyzer could be deemed "useful."

A yearlong study collecting and analyzing the exhaled breath of 18 marijuana smokers with a "simple to use" impaction filter device, produced by Swedish company Munkplast AB, could not consistently produce a positive result for cannabis usage one hour after a person lit up, according to researchers at NIST and the University of Colorado Boulder. These findings are consistent with decades of research on the topic.

"Our results do not support the idea that detecting THC in breath as a single measurement could reliably indicate recent cannabis use," the study published Monday says.

Developing a breathalyzer-style method of detecting recent THC usage and levels for individuals has been an area of interest for researchers as states across the country legalize recreational marijuana. The NIST and CU Boulder study recognizes that such a device in the hands of police could help "keep impaired drivers off the road."

Laying the groundwork for the development of such a device seems the goal of the study, which was funded through a $1.5 million grant from the Department of Justice's National Institute of Justice. Researchers will continue to draw on that financing, saying it will go toward another study that will collect more than 1,000 breathing samples from 40 participants, the organizations said in a statement.

"A lot more research is needed to show that a cannabis breathalyzer can produce useful results," said Kavita Jeerage, a materials research engineer and co-author of the NIST study. "A breathalyzer test can have a huge impact on a person's life, so people should have confidence that the results are accurate."

A roadside handheld breathalyzer for alcohol works by detecting ethanol vapors in a person's breath. But THC is present in exhaled breath in the form of an aerosol, which requires a different kind of method of collection than exists in any of the devices police currently use, the study says.

While methods to detect the presence of THC have been around since at least the 1970s, "consistent quantitative results across multiple studies have not been demonstrated," the study says.

The current study collected only 42 breath samples at a research facility and later in "a federally compliant mobile laboratory" positioned in a RAM ProMaster Cargo Van. Researchers took baseline breath samples including several weeks prior and 15 minutes before participants lit up, identified in the study as "baseline intake" and "baseline-experimental" samples, respectively. The "post-use" samples involved exhales taken one hour after participants smoked a "legal market" cannabis containing about 25% THC, according to the study.

"THC was identified in 31% of baseline-intake, 36% of baseline-experimental, and 80% of post-use breath extracts," the study says.

These one-hour-after-use results, collected via Munkplast's product, are "broadly comparable" to findings in other studies, researchers say. But they caution that the sample size was too small to support statistical claims. Moreover, the post- and pre-use results were somewhat unreliable.

"One hour after cannabis use, our results with the new impaction filter device are broadly comparable to previous pilot studies, considering participant characteristics and breath sampling differences," the study says.

"However, we must also consider that THC in breath at [one hour] post-use was not necessarily higher than baseline, even when THC in blood indicated compliance with the protocol and at least a five-fold increase immediately post-use," the study concluded.