Police officers in Pennsylvania and around the country generally take motorists into custody on suspicion of driving under the influence after conducting a breath test. Roadside toxicology tests are performed because the portable devices used are considered reasonably accurate and the link between blood alcohol concentration and intoxication is backed by solid science. However, determining whether or not a driver is impaired by marijuana presents both law enforcement and the scientific community with a far thornier problem. This is because police departments do not yet have a convenient and reliable way to measure THC levels in the blood and the science dealing with marijuana consumption and impairment is far more nebulous.

Scientists have developed a THC saliva test

Testing for THC is generally done by examining blood samples, but this is an expensive, time-consuming and invasive procedure. A THC breath test has been developed, but it is not considered accurate enough for police use because breath samples contain very low levels of THC. To overcome these shortcomings and drawbacks, a team of researchers from The University of Texas decided to create a roadside test that measures THC in saliva. The researchers claim that their saliva test produces accurate results when a milliliter of a driver’s blood contains just 100 picograms of THC.

Cheek swabs, testing strips and electronic readers

To perform the THC test, a police officer first uses a cheek swab to gather a saliva sample. The swab is then rubbed on a testing strip covered in an antibody that binds to THC. The final stage of the test involves placing the testing strip in an electronic reading device. According to the researchers, a police officer can perform the test and process the results in about five minutes.

Challenging toxicology evidence in marijuana-related DUI cases

The problem facing prosecutors is that accurate THC toxicology evidence may be of little practical use. This is because the link between THC levels and impairment is not clear, and an individual who consumes marijuana daily could be unaffected by THC levels that would leave a casual user of the drug barely able to function. If you have been charged with a marijuana-related DUI, an experienced criminal defense attorney could argue in court that it is not possible to prove intoxication beyond a reasonable doubt based on toxicology evidence alone.