Law enforcement agencies in Minnesota and around the country use portable breath-testing devices to determine whether or not motorists are operating their vehicles under the influence of alcohol, but there is currently no reliable test that police officers can use to identify marijuana impairment. However, that may soon change. Efforts to develop a marijuana breath test have received little support in the scientific community because THC levels in breath samples are low, but a team of University of Texas researchers believe that testing saliva would avoid this problem and produce more accurate results.

The researchers have developed a marijuana intoxication test that uses sensor strips to gather saliva from cheek swabs. The strips are coated with an antibody that binds with THC and isolates the cannabinoid from other compounds found in saliva. THC blood concentration is then measured by placing the strips in an electronic reader. During laboratory experiments, the saliva test has been able to accurately measure THC concentrations as low as 100 picograms per milliliter and as high as 100 nanograqms per milliliter.

If the saliva test proves successful in field testing, it could give police departments a valuable tool in the fight against impaired driving. THC levels are usually determined using blood samples, but blood tests are invasive, time-consuming and expensive. According to the researchers, the saliva test can be performed in five minutes or less by police officers who have received minimal training.

Experienced criminal defense attorneys may question the reliability of THC evidence in DUI cases even when tests have been performed correctly and their results seem accurate. This is because there is no firm scientific consensus regarding the connection between THC levels and impairment. Attorneys may argue that proving guilt beyond reasonable doubt is impossible when all prosecutors have to support impaired driving charges is THC evidence.