The increasing legalization of both recreational and medical cannabis across the United States has led to new questions about how to measure and manage THC impairment on roadways. Breath tests are one proposed method to test for such impairment, but the results of these tests don’t necessarily correspond to the level of cognitive and psychomotor impairment an individual is experiencing, especially as metabolites of THC may remain in the body up to weeks after the last use of cannabis. Researchers at Massachusetts General Hospital have sought a more reliable method for measuring impairment from THC consumption, and have developed a possible solution using brain imaging as an alternative to breath analysis.
The researchers tested an imaging technique known as functional near-infrared spectroscopy (fNIRS) to determine whether it could be used to identify signs of THC intoxication in the brain. The researchers conducted fNIRs brain imaging on 169 cannabis users before and after receiving either oral THC or a placebo, and compared the results of participants who reported being intoxicated with those of participants who reported low or no intoxication. In participants who reported intoxication after consuming the THC, the researchers observed increased oxygenated hemoglobin (HbO) concentrations from the prefrontal cortex region of the brain compared to those who reported low or no intoxication.
In combination with the self-reports, impairment was also measured through clinical ratings and heart rate. Senior author and principal investigator A. Eden Evins stated that machine learning models, using only information from the fNIRS data, could match the self-reports and clinical assessments of impairment 76% of the time. Because the fNIRS device is portable and noninvasive, it could potentially be used by law enforcement officers to assess drivers in the field. The devices could also be incorporated into a headband or cap for easier operation in the field, and can transmit data wirelessly to wearable recording units or laptops. This work was published in the journal Neuropsychopharmacology.
“Companies are developing breathalyzer devices that only measure exposure to cannabis but not impairment from cannabis,” said lead author Jodi Gilman, an investigator in the Center for Addiction Medicine at Massachusetts General Hospital. “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. While it requires further study, we believe brain-based testing could provide an objective, practical and much needed solution.”
While the study did not specifically assess fNIRS in the context of roadside assessments, the researchers believe it opens up possibilities for future development of brain-based testing measures for accurately determining THC impairment. This is important as previous research has shown that cognitive and psychomotor impairment from THC could double the risk of a fatal motor vehicle accident. The fNIRS study was funded by the National Institute on Drug Abuse.