Marijuana Intoxication: Are Sobriety Tests and THC Levels Reliable Indicators?

April 20, 2021 — A study performed by NIJ-supported researchers from RTI International found that THC levels in biofluids (i.e. blood, urine, and oral fluid) were not reliable indicators of marijuana intoxication for study participants.

Study participants were given specific doses of cannabis through different modes of ingestion (edibles and vapes), and researchers examined how that affected THC levels in the body, as well as performance on impairment tests.

"Each of the [20] participants completed all six dosing sessions," states an article from NIJ. "They ate cannabis brownies with 0, 10 mg, and 25 mg of THC and inhaled vapor containing 0, 5 mg, and 20 mg of THC. The dosing sessions were spaced at least one week apart."

Participants were given common impairment tests, including a paced serial addition test, divided attention test, and standardized field sobriety tests such as standing on one leg and eye tracking. "Study participants' cognitive and psychomotor functioning were negatively impacted after all oral and vaped doses of cannabis except for the lowest vaped dose, which contained 5 mg THC," says the NIJ article.

Vaped THC doses over 5 mg produced peak cognitive and psychomotor effects from zero to two hours after administration. The effects returned to baseline after four hours.

Oral THC doses over 5 mg produced peak cognitive and psychomotor effects after five hours and returned to baseline after eight hours.

"The researchers reported that the one leg stand, walk and turn, and modified Romberg balance tests were not sensitive to cannabis intoxication for any of the study participants," the NIJ article states.

Researchers collected biofluids before dosing and then nearly every hour for eight hours. "Results from the toxicology tests showed that the levels of all three targeted cannabis components (THC, cannabidiol, and cannabinol) in blood, urine, and oral fluid did not correlate with cognitive or psychomotor impairment measures for oral or vaporized cannabis administration," said the NIJ.

You can read the full NIJ article, and access the study's final report, here.

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