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New Study Says There Is No Scientific Basis For Current Marijuana DUI Laws

Currently, six of the states that have legalized marijuana in some fashion use threshold-based blood tests to determine whether or not a driver is under the influence. Blood tests are these states’ primary tool in prosecuting marijuana-related DUI charges.

The American Automobile Association, better known as AAA, just released findings from a new study. Researchers found that the THC limits dictating current marijuana DUI laws have no scientific basis. Commissioned by the Automobile club’s safety foundation, the study states it is impossible to determine someone’s level of marijuana impairment simply from a threshold-based blood test. Now AAA is saying we need to reform these laws.

In five of the six states, a positive THC blood test is enough to presume guilt in a DUI case, meaning you’re guilty if you test positive and not guilty if you pass the screening. AAA’s new findings suggest some intoxicated drivers may be going free just because of a flawed test while drivers who are safe to drive may are being prosecuted for DUI.

Courtesy of AP

Instead of using the blood test as a singular identifier, the organization recommends training police officers to go through a detailed step-by-step process to determine whether a driver is stoned or not. The blood tests would still be used, but only to test for marijuana’s presence in the blood to back up an officer’s suspicion, rather than as the primary indicator of guilt. Pennsylvania, Ohio, Colorado, Nevada and Montana currently employ the threshold-based blood tests, and with a slew of states gearing up to pass new legal marijuana initiatives, the issue could grow worse if those new states also implement these potentially harmful practices.

Marshall Donney, the organization’s President and CEO, addressed the issue when he said, “There is understandably a strong desire by both lawmakers and the public to create legal limits for marijuana impairment in the same manner we do alcohol. In the case of marijuana, this approach is flawed and not supported by scientific research.”

Trying to apply the same procedures we use with alcohol intoxication testing is pointless because the two drugs interact with our bodies in very different ways. The problem with marijuana blood testing lies in determining whether a positive test means the driver was impaired at the time of the incident or had simply used the drug in recent days, or even weeks.

Tolerance plays a significant role, as there’s not currently a scientific way to test whether someone is impaired (or the degree of the impairment) solely based on the THC content of their blood. If in an individual in question is a regular smoker, then an elevated level of THC in the blood stream may not indicate intoxication. On the other hand, a first-time smoker may have very trace amounts of THC in their system while still feeling very high due to their low tolerance. Even though the first-time smoker may not test positive on a threshold-based THC screening, the effects may be enough to impair their driving seriously.


Another major issue is that some states have zero tolerance policies attached to THC blood tests. These tests also pick up on the microscopic metabolites left behind by THC, meaning you could be charged with a DUI for testing positive even if you haven’t smoked in weeks. Mark A. R. Kleiman, an NYU professor and expert in the field of drug and criminal policy, claims this makes no sense. Kleiman recently said, “A law against driving with THC in your bloodstream is not a law you can know you are obeying except by never smoking marijuana or never driving.”

Kleiman cites the overstated effects of marijuana impairment as the main reason we should scrap weed-related DUIs altogether for a decriminalized system where the offense would only carry the punishment of a ticket. He cited a separate study claiming marijuana impairment raises the risk of an accident by double. Comparatively, a .12 blood alcohol content multiplies your risk of crashing 15-fold. A distraction as common as a crying baby in the backseat is considered as dangerous as marijuana impairment while driving, according to the study. The real problems occur when marijuana is mixed with other substances like alcohol, amplifying the effects of both on the driver. The AAA released a separate report on the effects of combining alcohol and marijuana that makes for an interesting read.

I would think this goes without saying but don’t get high and drive, regardless of what some research study “finds.”

Header Image Courtesy of Karen Roach

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