Recent Study Casts Doubt on THC Saliva Tests

By Paul Gaita 06/20/14

A positive THC test doesn't necessarily indicate recent marijuana use.

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A clinical trial in Oslo, Norway has underscored the central argument for critics of oral fluid drug tests: the presence of THC in saliva is not necessarily indicative of recent marijuana use.

Researchers collected oral fluid samples twice a day from habitual cannabis consumers during a prolonged period of monitored abstinence from the drug. They discovered that THC could be found in the test subject’s oral fluid for a period of up to eight days after their last exposure to cannabis. Furthermore, the study revealed that THC levels varied greatly during the period, revealing both positive and negative results at different times, despite the test subjects’ continued abstinence. The researchers concluded “these results are of great importance when THC results from oral fluid analysis are to be interpreted.”

The study has cast further doubt on the efficacy of such tests as a viable alternative for roadside checks for the presence of alcohol or other drugs. At the core of the argument is the fact that THC is processed through the brain through the nervous system and not the salivary glands, which would result in an inaccurate test response.

Critiques such as these, from various medical professionals, drug testing experts and even the U.S. Department of Justice, which declared that saliva tests “[do not] indicate… frequency, or amount of use, or impairment,” spurred the Michigan House of Representatives to drop a hotly debated bill provision that would give police the right to administer roadside saliva tests.

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Paul Gaita lives in Los Angeles. He has contributed to the Los Angeles Times, Variety, LA Weekly, and The Los Angeles Beat, among many other publications and websites.