What is Maine law on operating a motor vehicle with marijuana or THC?

Maine law does not prohibit consuming cannabis or marijuana and driving. Maine law prohibits driving under the influence of cannabis or THC. THC is the psychoactive ingredient in cannabis. Unlike alcohol, where the Maine legislature set a pre se limit of 0.08 as the per se limit for operating under the influence, the legislature has set no per se limit for cannabis or THC in a person’s blood.

The National Highway Traffic Safety Administration (NHTSA) has recognized it is difficult to set a per set limit for operation when it comes to cannabis. “It is difficult to establish a relationship between a person's THC blood or plasma concentration and performance impairing effects. Concentrations of parent drug and metabolite are very dependent on pattern of use as well as dose. THC concentrations typically peak during the act of smoking, while peak 11-OH THC concentrations occur approximately 9-23 minutes after the start of smoking…. It is inadvisable to try and predict effects based on blood THC concentrations alone….” NHTSA Drugs and Human Performance Fact Sheets.

Maine law defines driving “under the influence” of THC as meaning that a person’s mental or physical faculties are impaired at all, to any extent, by THC at the time of driving. Because there is no per se limit for THC in Maine, law enforcement looks to operation, behavior, and field sobriety testing to determine probable cause to arrest for driving under the influence of cannabis. If probable cause to arrest is determined, law enforcement will have a DRE (Drug Recognition Expert) evaluate the driver (at the police station) to reach an opinion on THC impairment. A blood or urine sample will be requested at the conclusion of this evaluation.

Cannabis OUI cases can be challenged in court and before the BMV. THC is different than alcohol. Most field sobriety testing has been developed to detect alcohol impairment not THC. The effects of THC peak within 10-30 minutes after smoking and the “high” typically lasts for 2 hours. The average person returns to “normal” or baseline functioning within 3-5 hours after smoking. However, a blood test can detect THC compounds in a person’s system for weeks.

In 2017 NHTSA reported to Congress that THC and blood levels are poor indicators of whether a driver is impaired or not impaired. “While fewer studies have examined the relationship between THC blood levels and degree of impairment, in those studies that have been conducted the consistent finding is that the level of THC in the blood and the degree of impairment do not appear to be closely related. Peak impairment does not occur when THC concentration in the blood is at or near peak levels. Peak THC level can occur when low impairment is measured, and high impairment can be measured when THC level is low. Thus, in contrast to the situation with alcohol, someone can show little or no impairment at a THC level at which someone else may show a greater degree of impairment.” NHTSA Report to Congress.