Why Saliva Drug Tests Don’t Work

When behind the wheel, sobriety is of utmost importance since your life and that of other road users is at stake. For this reason, several states across the United States have explored the idea of sanctioning the police to carry out oral fluid tests, primarily at the roadside, as a way of determining prior use of cannabis. But, even with the ongoing effort by law enforcement agencies to discourage drivers from driving under the influence of marijuana or while impaired, the behavior is still prevalent.

To make matters worse, recent studies have cast doubt on the effectiveness of saliva drug tests in detecting cannabis use. As a result, many questions have emerged on whether the techniques or devices used by law enforcement officers to test for drug use meet the correct criteria for roadside implementation. If you are wondering why saliva drug tests do not detect prior cannabis use as they ought to, read on:

Shorter detection window compared to other tests

In 2016, the Journal of Analytical Methods in Chemistry revealed that saliva/oral fluid testing devices were unable to detect prior cannabis use more than 50% of the time. Italian researchers used 20 subjects to determine the capacity of oral fluid tests to detect THC presence in the bloodstream. The participants said that they had used cannabis about half an hour to 24 hours before being tested.

According to the investigators, saliva testing technology only identified the presence of THC in 8 out of the 20 subjects. Other tests like urinalysis managed to identify 18 participants as having used cannabis before taking the test. The study supported other evaluations suggesting that mouth swab tests lack the necessary sensitivity to THC presence in the body after two to three hours of cannabis use. This means that cannabis users can pass the saliva drug tests while still being impaired.

Dusseldorf, Germany-based researchers also conducted a study involving 15 participants to evaluate their driving performance in a simulated environment after consuming three cigarettes of cannabis. Three hours after cannabis use, the subjects showed slight changes in their driving performance, including increased weaving cases. However, the driving style and performance of the participants almost matched their baseline performance past the three hours.

Failure to meet acceptable accuracy and sensitivity standards

Canadian researchers conducted a systematic review to assess the detection performance of on-site oral fluid test devices.  They went through eight databases, including Scopus, CINAHL, Engineering Village, Compendex, PubMed, Embase, MEDLINE, and Web of Science, to recognize studies that had looked into the effectiveness of devices used for testing oral fluid. The review used fifteen articles, which had leverage on-site testing technology in detecting the use of cannabis.

Findings from the review suggested that the existing devices are not adequate for detecting impairment, as they fail to meet the set accuracy and sensitivity standards. Furthermore, low THC concentration testing devices performed better in terms of accuracy, sensitivity, and specificity compared to those with the potential of detecting higher concentration levels.

From the above studies, it is evident that on-site saliva drug tests have a limited potential of detecting cannabis. After two to three hours of cannabis use, determining prior use of cannabis becomes challenging. However, technology advances in this space may help come up with more effective devices for accurate on-site drug detection.


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