Massachusetts is one of twenty-nine U.S. states, plus the District of Columbia, that now legally allow marijuana for recreational or broad medical uses or both (full list of these states available here). The Massachusetts Executive Office of Public Safety and Security (EOPSS) recently launched a public safety campaign, Drive Sober or Get Pulled Over, to warn and inform the public about the impairments that marijuana causes in drivers and the increased driving danger when alcohol and marijuana are combined. Marijuana is proven to impact the brain’s ability to function properly. Marijuana’s primary psychoactive ingredient, tetrahydrocannabinol (THC), has been shown to slow reaction times, impair coordination, and decrease decision-making ability.
One challenge for enforcement regarding marijuana use and driving is that impairment from marijuana is more difficult to measure than impairment from alcohol. There is currently no proven equivalent to an alcohol type breathalyzer test that measures blood alcohol concentration (BAC) levels to assess drunk driving. Unlike alcohol that dissolves in water, THC dissolves in fat. As toxicologist Marilyn Huestis discussed in an NPR story, this means that that the length of time that THC lingers in the body varies more than with alcohol, and is influenced by factors such as amount of body fat, type of cannabis product consumed, and frequency of use. It also means that a person’s blood THC levels may not directly correlate to when they are most impaired. Some states such as Colorado, Washington, Montana and Pennsylvania, define marijuana impairment using blood THC levels to legally define when someone is too impaired to drive. The state regulations in Ohio and Nevada determine impairment by blood tests and urine tests.
The San Diego Police department, and other enforcement agencies in New York, Arizona, and Nevada, have been screening drivers for THC using a mouth-swabbing testing device (the Dräger DrugTest 5000), which can test for the presence of seven drugs, including marijuana. The marijuana test is for delta-9 THC, the active THC compound which creates the high from marijuana. Unlike other components of THC, delta-9 THC typically only stays in a person’s system for a few hours and not days or weeks. Stanford University researchers have been developing a saliva-based test for THC using magnetic nanotechnology. Recently, police departments have been pilot testing a handheld breathalyzer for marijuana detection from Hound Labs. The device measures delta-9 THC levels and is able to detect marijuana from either inhaling or edibles. Cannabis Technologies is also developing a marijuana breathalyzer. These THC detection methods are often used in conjunction with other field sobriety and impairment testing.
In Massachusetts, Drug Recognition Experts (DREs) are specially trained to detect impairment from drug use. A full DRE exam takes about an hour and includes physiological measures (blood pressure, pulse, eye exams), and performance measures (balance, coordination). As described in a 2016 Boston.com article Massachusetts and other states are now offering a less intensive training, Advanced Roadside Impaired Driving Enforcement (ARIDE), which is still a step above typical field sobriety training.
In a September 2017 Massachusetts Supreme Court decision, the Court found that police cannot use standard field sobriety tests to determine definitively that a driver is too high to drive. The court determined that the standard sobriety tests were developed to evaluate alcohol intoxication and there is not yet sufficient evidence that they are indicative of marijuana intoxication. Under the ruling, police officers can still conduct field sobriety tests and testify about their observations regarding a driver’s demeanor and ability to perform physical coordination and mental tasks.
Dr. Michael Millburn, a Psychology professor at UMass Boston, has been developing a smart device app to assess driver impairment called DRUID. This app has been designed to measure cognitive and behavior impairment from marijuana, alcohol, prescription drugs and other brain-based contributors to impairment, such as fatigue. It contains a series of four different tests for reaction time, errors in decision making, motor tracking, and time estimation and balance. The app then integrates the results of each of the individual tests into an overall impairment score. The tests are completed in 5 minutes total. The app was developed to help people assess their own impairment, but could also be adapted for police use. The app is currently being tested at Brown Medical School. Research shows that some types of marijuana have non-linear patterns of impairment following consumption. Apps such as this could be useful for supporting driver safety and important complements to other tools and tests for measuring THC, alcohol, and other substances that can impair driver performance.
Written by Tracy Zafian, UMTC Research Fellow