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Too High to Drive? A New Way to Measure THC Impairment

Harvard researchers believe they've solved a problem that has plagued law enforcement and employers.

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One of the seemingly unsolvable puzzles for law enforcement and employers has been finding a reliable way to detect if someone is THC-impaired. 

A breathalyzer test can tell officers if someone is too intoxicated with alcohol to drive. Companies use blood and urine tests for on-the-job or pre-employment screenings to detect illegal narcotics in a person’s system. But THC impairment (aka as being high) is harder to track. The compound can be detectable in your blood and urine long after its psychoactive effects have worn off. 

The result has been chaotic. Officers arresting drivers for a pre-roll they enjoyed weeks ago; organizations and companies dropping marijuana-testing completely; or firing employees for using medical marijuana when not on the clock.

But a Harvard University-led research team believes it has found a solution. They recently published their findings in the journal Neuropsychopharmacology.

RELATED: Will Brain Scans Replace Breathalyzer Tests for Determining Cannabis DUI?

A new direction in impairment testing

Rather than relying on blood and urine like traditional drug tests, researchers at Massachusetts General Hospital used imaging technology as a non-invasive way to look for activation patterns in the brain associated with cannabis use.

They believe the research could make highways and workplaces safer. It also could keep employers from unjustly penalizing workers for past use of weed, including medical marijuana.

Jodi Gilman, an investigator in the Center for Addiction Medicine at Massachusetts General and an associate professor of psychiatry at Harvard Medical School, told the Harvard Gazette that the research marks a new direction for impairment testing.

“Our goal was to determine if cannabis impairment could be detected from activity of the brain on an individual level,” Gilman said. “This is a critical issue because a ‘breathalyzer’ 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.”

RELATED: A Breathalyzer Test For Cannabis? These Scientists Think They Have It

Measuring brain activation caused by cannabis 

The challenge in measuring marijuana impairment revolves around the fact that the amount of THC in the body does not correspond with functional impairment. But because THC can cause impairment, researchers want to find a way to determine if people are, for example, too high to drive a car or operate machinery at work.

To do this, they are looking at how the brain reacts to cannabis use.

The study involved 169 people who researchers gave either oral THC or a placebo. Those who reported becoming intoxicated by the THC had an increase in oxygenated hemoglobin concentration, a neural activity signature from the prefrontal cortex region of the brain. The growth was notably higher than those who reported low or no intoxication.

Detecting the level of oxygenated hemoglobin concentration in the prefrontal cortex is not as difficult as reading those words all together might suggest. The Massachusetts researchers wrote that testing equipment could fit into a lightweight, battery-powered device suitable for roadside tests.

They also wrote it’s possible to incorporate the technology into a headband or cap, eliminating the need for extensive set-up time.

While Massachusetts General Hospital and Harvard say they want to do more testing, they believe they are on the right track.

“Companies are developing breathalyzer devices that only measure exposure to cannabis but not impairment from cannabis,” Gilman said. “We need a method that won’t penalize medical marijuana users or others with insufficient amounts of cannabis in their system to impair their performance.

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