The work group on cannabis and driver impairment convened by the Bureau of Motor Vehicles should be applauded for thoroughly evaluating this issue. However, while well intentioned, the group’s majority recommendation around blood tests as “evidence of impairment by marijuana” is flawed.
Blood testing works for alcohol impairment, but not for marijuana.
When you are driving under the influence of alcohol, the law clearly says if you “blow” a .08 using a breathalyzer device, it is evidence that you are impaired and no further evidence is required.
The work group suggests that a similar limit be applied for THC, the psychoactive component in marijuana. Except this “limit” would not be as black and white. The group’s recommendation suggests that if a driver has 5 nanograms or more of THC in his or her system, it allows a judge or jurors to draw a “permissible inference” that the driver is impaired. (The group’s minority report suggests that other indicators of guilt such as a failed field sobriety test be required before a driver can be charged with impaired driving.)
We struggle with this for a few reasons. First, the science is not clear that 5 nanograms of THC per liter of blood consistently indicates impairment in the majority of users. Secondly, to apply such a legal standard to THC and not all other legal drugs, such as opiates, perpetuates the false perception that cannabis is somehow more dangerous. Finally, setting an arbitrary limit certainly makes us feel like we are “doing something” to keep impaired drivers off the road, but the reality is that adopting these recommendations will put innocent people at unnecessary risk of prosecution.
No magic number.
We know through scientific study that some cannabis metabolites may be present in the blood for many hours after a single use, long after any significant psychoactive or performance impairment effects are present. Someone who is using cannabis therapeutically will presumably have a higher baseline level of THC present in their blood at all times, but without any demonstrable impairment.
Science simply does not support the 5 nanograms limit as a measure of impairment. Some of the 89 studies and reports that the work group considered conclude that 2 nanograms is the right number; others suggest that much higher thresholds may be acceptable.
This year, researchers at the University of Iowa conducted a study of cannabis, alcohol and driving and found that “drivers with blood concentrations of 13.1 ug/L (the equivalent of 13 [nanograms] per milliliter) THC showed increased weaving that was similar to those with a .08 breath alcohol concentration, the legal limit in most states.”
So what, then, is the right number? Is it 2 nanograms? 5 nanograms? Or is it 13 nanograms?
Science over speculation.
Even the national standard of .08 BAC (blood alcohol content), now generally accepted when it comes to driving, is an arbitrary line in the sand — at .08, some people show minimal obvious impairment, while others are noticeably impaired at much lower levels. We as a society have decided that we will now accept the .08 limit for everyone. But it wasn’t always that way.
For most of the 20th century, 0.15 percent was the commonly used standard, a level settled on in 1938, two years after the invention of the pragmatically named “ Drunkometer” allowed breath testing for alcohol concentration in the blood.
As recently as 1998, only 16 states and the District of Columbia had adopted the .08 BAC standard. Yet, it was made the national standard in 2000.
Cannabis, however, is not alcohol. It is variably impairing, with newer users more likely to manifest impairment at lower doses. And researchers have yet to create a successful, roadside breath and saliva test for cannabis. And even if a cannabis breathalyzer existed, it still would not answer the question of “how much is too much?”
Maine is nationally recognized for its successfully regulated medical cannabis program. It is understandable that, given the increased acceptance of marijuana, legislators will seek to implement stringent safety regulations.
The smart approach would be to hold off on enshrining any specific nanogram level in law. Instead, the state should focus on public education and increasing the effectiveness of law enforcement in this space.
To avoid an ugly blot on an otherwise respected program, the Criminal Justice Committee should rethink the wisdom of letting fear, not science, determine policy.
Catherine Cobb formerly served as the director of Licensing and Regulatory Services for Maine’s Department of Health and Human Services where she was instrumental in the creation of Maine’s medical marijuana program. Cobb, now retired, is the secretary of the board of directors for the Wellness Connection of Maine.