Police departments in New Mexico and around the country equip their officers with portable breath-testing devices to find out whether or not drivers are operating their motor vehicles while under the influence of alcohol, but there is no such device capable of reliably identifying marijuana impairment. Efforts to develop a THC breath test have been largely unsuccessful because breath samples contain very low levels of the cannabinoid, but a team of University of Texas researchers believe that they have found a way around that problem.

The researchers say that they have developed a saliva-based THC test that works even when saliva samples contain microscopic quantities of the cannabinoid. To perform the test, police officers would gather saliva samples using cheek swabs and then transfer the collected saliva onto testing strips coated with an antibody that binds to THC. The results are provided by an electronic reader that the testing strips are inserted into. The researchers shared their findings online using a platform provided by the American Chemical Society.

Law enforcement has been asking for a reliable THC test for several years, and those calls have grown louder recently as several states have passed laws legalizing marijuana for recreational use. Currently, THC testing is done by collecting blood samples, which is time consuming, complex and invasive. However, a test may prove to be of little practical use to prosecutors as the science linking THC levels with impairment is far from clear.

Motorists are generally charged with DUI when blood samples reveal between one and 15 nanograms of THC per milliliter. Experienced criminal defense attorneys may seek to have such charges dismissed due to the scientific ambiguity surrounding THC impairment. Attorneys could also question the results of alcohol toxicology evidence in drunk driving cases if the equipment used was not maintained properly or their clients suffer from a medical condition known to influence breath-test results.