Marijuana DUI Laws Do Not Require Actual Impairment

Filed under: DUI by Contributor @ July 21, 2016


With more states across the country gradually legalizing marijuana use for either medical or recreational purposes, laws aimed at regulating driving while under the influence of marijuana have become an increasingly important issue. Currently, Pennsylvania’s driving under the influence of marijuana statute is very similar to its law prohibiting driving under the influence of alcohol because a blood test is used to determine the amount of THC in the driver’s body. If the amount of THC is higher than the established threshold, then the driver will likely be convicted. However, some groups, including the American Automobile Association’s (AAA) safety foundation, have criticized laws like this because a study conducted by AAA found that there was no possible way to set a blood-test threshold for THC that can reliably determine a particular driver’s impairment.

Marijuana affects people differently based on a number of factors, including frequency of use, and there is no scientific evidence that can prove that all drivers become impaired at a certain level. Because of this, and because of the threshold system currently in place, AAA claims that people who are driving dangerously after using marijuana may go free as long as they’re under the threshold, and people who are driving safely long after marijuana use may be wrongfully convicted simply because their THC level was above the set limit. While this may be true across the country, my personal opinion is that the level of THC in blood required to violate Pennsylvania’s DUI statute is so low that the practical effect is that anyone who has smoked marijuana in the 10 days prior to driving, and often much longer, will be arrested if their blood is tested, due to the residual levels remaining in the blood, despite the fact that the driver is in no way impaired by the substance at the time. Indeed, determining if a driver is impaired from marijuana at the time of a traffic stop, as opposed to simply having used it some time ago, is a much more complex process than the tests used to determine impairment from alcohol.

Complicating the matter further is the fact that THC will remain in a frequent user’s body longer than it will in someone who uses less frequently. This means that an occasional user may be impaired at the time of a traffic stop, but by the time police transport them to the hospital and obtain a warrant to take their blood, the THC in their blood may have dissipated to a level below the threshold. Conversely, a frequent user may not be impaired at all at the time of a traffic stop, but if their blood is tested, the simple fact that they have used marijuana in the past may leave them liable for DUI. Further still, Pennsylvania’s DUI statute criminalizes the presence of metabolites of marijuana in the driver’s blood, and these metabolites can remain in a marijuana user’s blood for weeks after the effects of the substance have worn off.

Considering that a defendant convicted of a first offense DUI for marijuana use can be liable for up to a six month-jail term, up to a $5,000 fine, and one-year license suspension, many have pushed for reform of DUI statutes like Pennsylvania’s because of the inherent unfairness of convicting a person for DUI when they weren’t actually impaired while driving. The AAA safety foundation instead suggests a system in which specially-trained police officers will screen a driver for varying symptoms of drug use, such as pupil dilation and abnormal behavior, in addition to the presence of THC. Others have even suggested making it a traffic violation instead, citing studies that show driving while talking on the phone with a hands-free device is twice as likely to cause an accident than driving after using marijuana, and driving with a BAC of .12, which carries lower penalties than driving with THC or marijuana metabolites present in a blood sample, is more than seven times more likely to cause a crash than driving after using marijuana.

Pennsylvania’s recent legalization of medical marijuana may cause even more pressure to reform the DUI statute. As it stands, a person who is subjected to a traffic stop several days after legally using medical marijuana could be convicted and face the same penalties as someone who was driving under the highest grade of alcohol impairment.

Considering the unreliability of blood tests in determining the actual impairment of a driver who has used marijuana in the past, do you think the law should be amended? Let us know in the comment section below.


  1. Jason says:

    Yes…I am currently battling such a case. How can I be convicted of something that has no factual scientific evidence backing up the charge?

  2. The idea behind the law that makes it illegal to drive with any byproduct from smoking marihuana in your system is that it is rationally related to protecting the safety of drivers on the roadways of Pennsylvania. Thus, even though there is no direct correlation between banning people who smoked marihuana weeks earlier from driving and the safety of other people on the road at the time of driving, while fully sober, the law has been found to be constitutional. So the District Attorney doesn’t need any factual scientific evidence to win. Not that you shouldn’t still challenge this type of case, as things may change in the future, but for now this is the law in Pennsylvania.

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