Research Could Lead to Reliable Marijuana Breathalyzer

Driving under the influence of marijuana is illegal in any state, but to enforce the law, authorities need a reliable roadside test for marijuana intoxication. More research will still be needed to understand how breath levels of THC correlate with blood levels and what blood levels of THC indicate impairment.

The National Institute of Standards and Technology reports that some of its scientists have measured a fundamental physical property of the main psychoactive compound in marijuana, delta-9 tetrahydrocannabinol (THC) -- they measured its vapor pressure. This is a measurement that, due to the compound's chemical structure, is very difficult and had not been accomplished before, NIST announced July 5, saying the results have been published in Forensic Chemistry.

Some companies have been working to develop marijuana breathalyzers, but testing someone's breath for marijuana-derived compounds is far more complicated than testing for alcohol, the agency reported, explaining that driving under the influence of marijuana is illegal in any state, but to enforce the law, authorities need a reliable roadside test for marijuana intoxication.

"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."

According to the agency's article, Lovestead is not designing a breathalyzer herself, but "she and her colleagues are laying the technical groundwork for manufacturers to develop accurate devices. While this research is an important step forward, more research will still be needed to understand how breath levels of THC correlate with blood levels, and what blood levels of THC indicate that a person is too impaired to drive." Their paper was published online June 27.

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