How Long Should a Marijuana User Wait Before Safely Operating a Car?

It can be difficult for a marijuana user to subjectively assess their level of impairment. Even worse, there is no way for a marijuana user to objectively evaluate their level impairment. So, after consuming marijuana medically or recreationally, how can a marijuana user make a safe decision about driving?

Before we get to that question, let’s do a quick review of Michigan’s OWI laws as it relates to drugs. In Michigan, you can be charged (and potentially convicted) if you are either impaired or intoxicated by alcohol, drugs, or any combination thereof.  Specifically, Michigan’s OWI law references impairment or intoxication caused by alcohol, controlled substance or “other intoxicating substance.” See Michigan Compiled Laws Sec. 257.625.

Notably, the statute does not define either the word intoxicated or impaired, leaving that factual determination to the fact finder, which is usually a jury of 6 or 12 individuals, depending on if the case is a misdemeanor or a felony.  To assist the jury in reaching this determination they will be given several standard jury instructions.

As it relates to intoxication, M Crim JI 15.5 suggests that the jury consider the physical condition of the driver.  They are told to consider such things as whether their judgement, manner of walking, talking, etc. seems normal. If it’s not normal then the jury is asked to consider whether the prosecutor has shown that the abnormality was caused by the consumption of the alcohol, controlled substance or other intoxicating substance.

Unless yours is a zero tolerance case, simply consuming or smelling of marijuana is not enough. According to M Crim JI 15.2 the “test” is whether the consumption of the marijuana significantly affected the driver such that they could not operate their vehicle in a “normal manner.”

The issue of impairment is a little different. According to M Crim JI 15.3 the test for impaired driving is whether the driver was no longer able to operate their car like “an ordinary prudent driver” and that their driving was lessened to the point that it was noticed by someone else.

If there is a blood test showing the amount of THC in your blood, then the jury can consider this as well, provided they find that the blood test is reliable, and may give such test whatever weight they believe that it deserves.

In order to prevail at trial the government must show that the marijuana consumed either caused the requisite impairment or intoxication beyond all reasonable doubt.

With that understanding it should be even clearer now that a person who has used marijuana cannot subjectively decide if their ability to operate was either significantly affected or lessened to the point that they can no longer operate their car prudently. Which brings us back to the question of how long should a person who has consumed marijuana wait before driving? The only way to safely reach this determination is to wait longer than you think necessary, which of course begs the question “how long is necessary.”

Marijuana has not been studied nearly as extensively as alcohol, but to try to answer this question, scientists performed a meta-analysis of 80 science journal articles that addressed this topic.  The name of the paper is: Danielle McCartney, Thomas R. Arkell, Christopher Irwin, Iain S. McGregor, Determining the magnitude and duration of acute Δ9-tetrahydrocannabinol (Δ9-THC)-induced driving and cognitive impairment: A systematic and meta-analytic review, Neuroscience & Biobehavioral Reviews, Volume 126, 2021, Pages 175-193, ISSN 0149-7634.

A meta-analysis consists of performing a statistical analysis of the data contained in a large number of scientific papers. A meta-analysis produces a weighted average and tends to produce a more reliable conclusion then could be gleaned from any one paper.  It is a case of the whole being greater than the sum of its parts because the overall amount of data is combined.

In performing this analysis, the scientists were able to cull 1534 data points from the 80 papers reviewed, and from their analysis of same concluded that in most instances a marijuana user’s high lasts from between 4 and 10 hours depending of whether the marijuana is eaten or inhaled. The dose is important too, especially when inhaling marijuana, and for higher doses the high may last 6-8 hours.

The length of the impairment is also dependent on the complexity of the task. Marijuana tends to impact more complex tasks like driving for longer periods than it does for simpler tasks. The scientists also found that experience mattered. It was easier to predict length of impairment for occasional users than for chronic users.

As a rule of thumb, the scientists suggested that most users of marijuana could perform most of the tasks necessary to safely drive after 5 hours and that pretty much all driving related competencies returned after 7 hours.

If you have been charged with operating under the influence of marijuana, have one of the intoxicated driving lawyers at the Barone Defense Firm review your case. We will determine if the prosecutor might be able to prove their case at trial and also determine what defenses apply to your case.  The initial case review is free of charge.