A recent surge in the number of DUI cases involving motorists under the influence of marijuana is presenting law enforcement agencies in Virginia and around the country with a thorny problem, and this is especially true in parts of the nation where the drug is now legal for medical or recreational purposes. Police use breath-testing equipment to identify alcohol impairment, but attempts to develop a THC breath test have not met with much success because breath samples contain very small quantities of the cannabinoid.

Researchers say that they have now solved this problem by developing a THC test that uses saliva instead of breath samples. The test works by transferring saliva that has been gathered using a cheek swab onto testing strips coated with an antibody known to bind with THC. The strips are then inserted into an electronic reading device, which reveals blood THC levels in much the same way that portable breath-testing devices reveal blood alcohol concentrations. The University of Texas researchers claim that police officers will be able to complete the test in approximately five minutes.

The saliva test could be a real law enforcement breakthrough if it proves effective in field tests. The only way police departments can gather THC evidence currently is by drawing and testing blood. This presents several challenges. A search warrant is generally required to collect a blood sample, and the process is expensive, time consuming and invasive.

Experienced criminal defense attorneys may question the value of THC evidence in DUI cases even if it appears to be accurate. This is because marijuana affects individuals differently to alcohol, which means the amount of THC in a driver’s blood may not be a reliable indicator of impairment. When THC results are not supported by more compelling evidence, attorneys could seek to have DUI charges dismissed.