The Legislature is being urged to pass a law setting a blood-level limit that determines when someone is driving under the influence of marijuana.

Members of a study group made the recommendation Tuesday. They were split, however, on what level of THC in the blood would show impairment, with some members saying the scientific community is divided on the issue and uncertainty could lead to false convictions.

How to deal with impaired drivers is likely to become a more pressing issue as Maine considers joining four other states and the District of Columbia in legalizing marijuana for recreational use. A group is collecting signatures to get a proposal to legalize recreational use on the November 2016 ballot.

The working group was convened by the Legislature’s Joint Standing Committee on Criminal Justice and Public Safety in response to a bill submitted by the secretary of state. The measure would make it a crime to drive a car while having a THC level of 5 nanograms or more per milliliter of blood.

Other recommendations include setting a THC blood level to determine intoxication when marijuana is combined with alcohol, prohibiting drivers under 21 from having any THC in their blood while driving, and allowing license suspension of at least a year for young drivers who test positive for THC unless they are medical marijuana patients.


The group unanimously supported the use of approved, preliminary breath-alcohol testing devices by police officers to determine if a driver is intoxicated, and suggested that the number of specially trained drug recognition officers be increased.

The 20-member working group included police, prosecutors, representatives of the medical marijuana industry and marijuana legalization advocates.

Maine’s law against operating under the influence – OUI – already prohibits driving a motor vehicle while impaired by marijuana, but there is no specific breath or blood-level limit like there is with alcohol.

So far, six other states have set legal limits for the concentration of tetrahydrocannabinol – or THC, the psychoactive ingredient in marijuana – in the blood. Colorado, Washington and Montana have set an intoxication level of 5 nanograms or more of THC per milliliter of blood. The amount of THC in a driver’s system would be determined with a blood test.

Recent research into the effect of marijuana use on drivers is mixed, although many studies indicate drivers are less impaired by marijuana than by alcohol and tend to make fewer risky choices than drunken drivers. The National Institute on Drug Abuse maintains that marijuana significantly impairs judgment, motor coordination and reaction time, but other research shows drivers impaired by marijuana overcompensate by driving more slowly and avoiding passing other cars.

There is no simple roadside test for marijuana similar to the breath test used to determine blood-alcohol content. Police officers currently can use a drug recognition exam on the roadside – which includes examining the eyes – to detect impairment from drugs. But some say they need better tools to stop drugged driving as the culture becomes more accepting of marijuana use.


David Boyer, a group member and marijuana legalization advocate leading the push for a 2016 legalization vote in Maine, said it is worth noting that the group did agree on many aspects of the recommendations, but there wasn’t consensus when it came to the science behind determining impairment. He said some group members are concerned that regular marijuana users could be falsely convicted for driving while impaired because they build up a tolerance to THC. A heavy medical marijuana user, for example, could carry a THC level of 5 nanograms per milliliter and show no signs of impairment, he said.

“The science is clear with alcohol that .08 (percent) blood content means the vast majority of the population is impaired,” he said. “We don’t want patients that are perfectly aware and sober to be charged with DUI just because their nanogram level is above 5, which is somewhat of an arbitrary number.”

John Pelletier, chairman of the Criminal Law Advisory Commission, said the group engaged in a productive process despite “wrestling with a new area of the law.” He disagreed with the majority consensus that a level of 5 nanograms of THC per milliliter gives permissible inference that a person is intoxicated. He said some studies reviewed by the group indicate that 5 nanograms is “not an appropriate level,” while other studies fail to demonstrate a statistical link between THC in the blood and increased crash risk.

“If the science is uncertain but as a matter of policy we move in that area, the first attempt should be conservative,” Pelletier said.