Here’s How Long You Stay Impaired After Taking an Edible, New Research Suggests

Updated: Jun. 05, 2024

A new Canadian study illuminates surprising insights on how that "special" gummy impacts a sensitive activity. (Plus, breaking UCLA data on current cannabis usage rates.)

According to a 2023 survey by Gallup, 50% of Americans have tried marijuana—the greatest number on record since the global analytics and advisory firm started its annual survey in 2003. Meanwhile, today a UCLA study published in the Journal of the American Medical Association calculated cannabis use among 176,000 UCLA primary care patients to find that one in six said they smoke, vape, or ingest cannabis products to manage a stress, pain, sleep, or a medical condition.

In any case, experimentation has risen—the data hint that it’s possible half the guests you brush elbows with at parties this summer have tried marijuana at some point.

So a new study highlights that there’s no easy way to scientifically but efficiently determine whether an intoxicated driver has ingested marijuana the same way there is for alcohol. Restrictions around the levels of delta-9-tetrahydrocannabinol (THC), the psychoactive component of cannabis, in the blood are also largely based on smoking marijuana…but reports indicate that people are increasingly ingesting marijuana, such as through edibles.

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A May 2024 study published in the Journal of Cannabis Research (an international, peer-reviewed journal that’s affiliated with the Institute of Cannabis Research at Colorado State University-Pueblo) aimed to examine exactly how—and how long—eating an edible might affect someone who is driving.

For the study, a team of Toronto researchers specializing in pharmacology, toxicology, and psychiatry gathered participants between the ages of 19 and 79 who had a driver’s license for at least 12 months, drove at least once a month and who said they had ingested an edible at least once in the prior six months.

Participants were given edibles that contained about 7.3 milligrams (mg) of THC. Then, after two, four and six hours, participants used a driving simulator to measure differences in their driving behaviors after consuming the edible. The researchers also collected a blood sample before giving participants the edible sample, then again two hours later.

On average, participants drove slower two hours after ingesting the edible, but not after four or six hours. However, during check-ins with the researchers at each interval, participants also self-reported their experience being altered up to seven hours after edible consumption, and being less willing to drive up to six hours later.

When it came to driving impairment, the researchers did not observe that participants were “weaving” from left to right, increasing their speed, or demonstrating unusual changes in speed or reaction time after eating the edible. THC levels in the participants’ blood samples significantly increased after eating the edible, but they were still considered “relatively low,” according to the study, at 2.8 nanograms per milliliter two hours after consumption.

The study authors state that there was no correlation found between blood THC levels and “weaving” or increases in average speed, which they say aligns with recent research on smoked cannabis that indicates there isn’t a straightforward relationship between blood THC and driving impairment. “It may be possible that, for the smoked route, there is a threshold above which driving is impacted,” they write. “However, the present study suggests that blood THC may not be as useful for detection of impaired driving after edibles as it may be for the smoked route.”