Setting Legal Limits for THC in the Bloodstream: Are You Too High to Drive?

A proposed bill in Michigan, HB 4727, aims to set a legal limit on how much THC an individual can have in their system while driving. The proposed limit is 5 nanograms per milliliter of blood. This is a highly controversial topic, however: Because of how THC breaks down in the body, many experts opine that measuring the amount of THC in someone’s blood is not an accurate way of determining whether they are driving high.

How Is THC Metabolized?

THC dissolves in fat, in contrast to alcohol, which dissolves in water. Fatty tissues act like sponges for THC. The presence of THC in the bloodstream and how fast or slow it leaves your system are dependent upon how frequently marijuana is consumed. For example, someone who consumes marijuana frequently will have a constant level of THC present in their blood, even when they are no longer under the influence of marijuana. This is because the body’s fatty tissues have absorbed so much of the THC that it continues to leak into the bloodstream for weeks after they last consumed it.

Therefore, applying an arbitrary number would not be a reliable method of determining impairment. You could have non-frequent users of marijuana who are able to pass a blood test since the THC in their system would dissipate quickly; you could also have a frequent user of marijuana get charged for operating while intoxicated (OWI) even though he or she hasn’t consumed marijuana in weeks.

Marijuana and Driving Laws

While it is readily apparent that legislators desire to come up with a number that will establish a standard level of marijuana intoxication, such as the 0.08% blood alcohol concentration (BAC) standard for alcohol, it is extremely difficult to scientifically come up with one that would be a reliable indication of impairment for every consumer of marijuana. This is not to say that a more reliable method cannot be discovered that would indicate marijuana intoxication.

Driving under the influence of alcohol, marijuana, or any other drug is certainly an important public health issue, but setting an arbitrary limit that is not scientifically supported is risky. Many states have rushed to set a THC limit which has resulted in states essentially making up a number. Six states currently have laws setting forth a nanogram limit ranging between one to five nanograms of THC. Those states are Illinois, Montana, Nevada, Ohio, Pennsylvania, and Washington.

Have You Been Charged with an OWI?

While Michigan’s marijuana driving laws are still under debate, state residents continue to be charged with OWIs. If you have been charged, our defense attorneys at Grewal Law PLLC will fight to protect you from a criminal conviction. Put award-winning attorneys who know and understand the science of cannabis on your side.

Call (888) 211-5798 or fill out an online form to schedule your free, no-obligation consultation.