Harvard Researchers Develop New Way to Measure Cannabis Impairment

Harvard Cannabis Impairment - GCI Content Hub - Global Cannabis Intelligence

Harvard researchers study a practical way of measuring cannabis impairment which could make sobriety testing more fair and accurate.

A recent study reveals a new method to identify those whose performance is impaired by Tetrahydrocannabinol (THC), the primary psychoactive compound in cannabis.

THC can cause intoxication and impaired function, creating implications for traffic, workplace and other potential safety risks.

Why is measuring cannabis impairment important?

As jurisdictions across the globe liberalise cannabis use, an accurate tool that distinguishes between impairment and mild intoxication from THC is needed, particularly for road safety.

The study, published earlier this month in Neuropsychopharmacology (2022), examines the effectiveness of using functional near-infrared spectroscopy (fNIRS) for detecting individuals with THC impairment.

“There are currently no evidence-based methods to detect cannabis-impaired driving,” writes the study’s lead author, Jodi Gilman, investigator at the Centre for Addiction Medicine and associate professor of psychiatry at Harvard Medical School.

“This is a critical issue,” she explains, “because a ‘breathalyser’ type of approach will not work for detecting cannabis impairment, which makes it very difficult to objectively assess impairment from THC during a traffic stop.”

This is because breathalyser devices measure exposure to – but not impairment from – cannabis. Currently gold-standard field-sobriety tests are resource-intensive and may be prone to bias.

A reliable method to accurately measure THC intoxication is pivotal to prevent penalising medical cannabis users and those who have consumed insufficient amounts of cannabis to impair their performance.

How effective is the fNIRS method?

169 participants underwent the brain imaging procedure (using fNIRS), following the consumption of either oral THC or a placebo.

The research reveals fNIRS as a potentially highly effective technique for measuring THC-induced impairment empirically. fNIRS data determining THC-impairment matched self-reporting and clinical assessment “76 per cent of the time,” Gilman states.

Furthermore, fNIRS is a simple, portable imaging method to detect cannabis-impaired driving.

“Our research represents a novel direction for impairment testing in the field,” writes Gilman. “While it requires further study, we believe brain-based testing could provide an objective, practical and much-needed solution.”

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