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A test for marijuana impairment? A UMass prof has an app for that

A marijuana joint. Marcio Jose Sanchez/Associated Press

Massachusetts voters legalized recreational marijuana earlier this month, despite the fact that there’s still no easy way for law enforcement to test someone behind the wheel for marijuana-induced impairment.

A field sobriety test is used when a motorist is suspected of reckless driving, and a breathalyzer is used to gauge the level of alcohol in a driver’s bloodstream. But there’s nothing similar to a breathalyzer for testing whether someone is driving while under the influence of marijuana.

“You have to prosecute the person based on the officer’s observations and what the officer found during the car stop. It makes it very difficult,” said William G. Brooks III, Norwood police chief and president of the Massachusetts Chiefs of Police Association.


That’s why Michael Milburn, a psychology professor at University of Massachusetts Boston for 39 years, is trying to get his app that tests for marijuana impairment into the hands of law enforcement. He has created and self-funded DRUID, an acronym for for driving under the influence of drugs. It is a tablet-based app in which users are asked to perform a series of tasks in five minutes.

(Milburn’s DRUID app is not connected to a government-led consortium with the same acronym that was formed to provide scientific evidence to support European Union road safety policies.)

A balance test is one task on the app for drivers.Handout

The app tasks include asking users to tap the screen in certain places when they see different shapes; to stop a clock when 60 seconds have passed; to follow a moving circle on the screen with a finger as it randomly changes directions; and to stand on one leg for 30 seconds each with the iPad in one hand.

Milburn has run tests and had subjects use DRUID repeatedly while consuming marijuana and tracked impairment scores as they rise, and then decrease as the drug metabolizes. He has not published any peer-reviewed studies based on his tests.


“I could see marijuana legalization was coming eventually. Prior to now, people had no way to really know if they were impaired or not. One of my hopes in this is to create a responsible community of drug users,” said Milburn.

Milburn worries that people who know they shouldn’t drive after smoking marijuana will get behind the wheel too soon because they don’t feel impaired. The app costs 99 cents, and iPhone and Android versions are expected to be released in the next few months.

Recreational marijuana use in Massachusetts will be legal for adults 21 and older on Dec. 15, and marijuana retail stores are expected to open in 2018. But it’s not only the lack of a device to test drivers for marijuana impairment, but also the lack of an accepted standard, like the .08 blood alcohol content level that determines a person consuming alcohol is legally impaired to drive.

A study by the AAA Foundation for Traffic Safety has found that in Washington state, the proportion of drivers in accidents who tested positive for tetrahydrocannabinol (THC), the component that gives cannabis its psychological effects, rose from 20 to 30 percent between 2005 and 2014. Washington legalized medical marijuana in 1999 and its recreational use in 2012.

Massachusetts does not yet have a threshold for THC in the blood, unlike Colorado and Washington, which have set that threshold at five or more nanograms of THC per milliliter of blood.


But another study by the foundation found that a quantitative threshold cannot be scientifically supported, since people process THC differently.

“There’s no level at which there’s any kind of equivalency for a .08 BAC where a majority of people driving would be impaired,” said Lindsay Arnold, a research analyst at the Foundation for Traffic Safety.

That is partially attributable to the fact that, unlike alcohol, marijuana is fat-soluble and can be detected in a user’s body for weeks after use.

Saliva swab tests cost around $25 and check the mouth for marijuana and other common drug use in the past 24 to 36 hours. But even these tests can be unreliable, because they can detect marijuana use in the past eight days in some cases. No police department in the state is using the swab tests now, Brooks said.

“People have to figure out that THC in the saliva or THC in some sort of swab is indicative of recent marijuana use, and some level of THC is indicative of impairment,” said Brooks. “After that groundwork is done, [the testing] would be helpful. There’s a lot of work to be done.”

Christine Cunneen of Hire Image, a Rhode Island provider of drug testing services to employers, thinks chemical testing will come before an app like DRUID is used by law enforcement to test drivers.

“That’s the way it’s always been. There will be chemical testing that comes out, and to me, that’s more accurate.”


Hae Young Yoo can be reached at Follow her on Twitter @HaeYoung_Yoo.