Scientists are working on a reliable THC breath test

Jul 28, 2017 | drunk driving

Police in Ohio and around the country rely on portable breath-testing equipment and field sobriety tests to determine whether or not motorists are operating their vehicles under the influence of alcohol, but they do not yet have a reliable way to identify marijuana impairment among drivers. While blood alcohol levels can be scientifically linked with degrees of impairment, traces of THC can be detected in toxicology tests long after its intoxicating effects have dissipated.

However, the National Institute of Standards and Technology reported on July 5 that some of its researchers had made a major breakthrough in this area. The NIST scientists say that they have found a way to measure the vapor pressure of THC, which could help them to understand how the metabolite behaves when it transitions from a liquid into a gas. This is important for the development of any future marijuana breath test because devices like Breathalyzers analyze the chemical processes that occur when molecules leave the lungs and are exhaled as vapor.

The research has been published in the scientific journal Forensic Chemistry, but the scientists behind it are quick to point out that much still needs to be done before the nation’s police officers have a reliable way to test for marijuana impairment. While being able to accurately determine THC levels with a breath test may be a positive first step, scientists do not yet fully understand the relationship between the metabolite and impairment.

Criminal charges must be proved beyond reasonable doubt, and prosecutors generally meet this standard in drunk driving cases by introducing the results of breath or blood tests. Criminal defense attorneys may question the reliability of toxicology test results when the equipment used has not been properly maintained or strict procedures were not followed, and they may seek to have drunk driving charges dismissed entirely when breath or blood evidence has little or no scientific merit.