Researchers at the Johns Hopkins University School of Medicine, in a study supported by the National Institutes of Health’s National Institute on Drug Abuse, added to the evidence that the combination of edible marijuana and alcohol worsens impaired driving compared to either substance taken alone. The study also found that cannabis (alone or with alcohol) did not impair performance on standard field sobriety tests.
These findings were announced on May 1st. JAMA Networkhighlights the urgent need for widespread public education about the potential potentiating effects of the combination of cannabis and alcohol and improved roadside driver impairment detection methods. The study also found that the legal alcohol intoxication limit (0.08% breath alcohol concentration, or BrAC) in most areas of the United States is likely too lenient if a driver uses marijuana and alcohol together.
Our findings indicate that the combination of cannabis and alcohol causes significantly greater impaired driving and subjective intoxication than either substance alone. Importantly, these findings suggest that the interaction between cannabis edibles and alcohol is not merely additive, but may act synergistically in producing impairments that have important implications for real-world risk. ”
Dr. Austin Zamarripa, lead study author and assistant professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine
In this study, the research team used a rigorous, controlled design in which participants participated in several outpatient experimental sessions. During each session, subjects were given either a cannabis-infused brownie (10 or 25 mg of THC) or a placebo brownie, followed by an alcoholic beverage or a non-alcoholic placebo drink. The alcohol dose was adjusted for each participant to give BrACs of 0.05% or 0.08%.
Participants were healthy adults aged 21 to 55 years, ascertained through initial medical and psychiatric screening, physical examination, and periodic blood tests. Thirty participants were enrolled and randomized into the study, and 25 completed all study visits. All participants reported binge drinking within the past 90 days, having used cannabis and alcohol together within the past year, and limiting their cannabis use (less than three times per week, at least once in the past year) to reduce the effects of tolerance. Participants had no recent use of other illicit drugs as evidenced by urine drug testing.
After medical eligibility was confirmed through an initial screening visit, participants completed a second pre-study visit to familiarize themselves with the driving simulator and other performance tests to reduce learning effects in the experiment. After this training visit, participants completed seven experimental sessions in which they consumed cannabis alone, alcohol alone, cannabis and alcohol together, or placebo cannabis and placebo alcohol. Session order was carefully balanced across participants to ensure unbiased results.
At each pre-dose experimental session, participants completed baseline assessments including simulated driving, standard field sobriety tests, cognitive/psychomotor performance tests, subjective drug effects questionnaires, and blood samples to measure THC and THC metabolite levels. Participants consumed either a cannabis-infused brownie or a placebo brownie 1 hour after breakfast, and 45 minutes later they consumed an alcoholic beverage or a placebo drink (which provides a sensory stimulus similar to an alcoholic beverage to maintain dose blinding) over a 15-minute period. Participants completed the same set of driving and other assessments repeatedly throughout the day for up to 7.5 hours after consuming the brownie. Study sessions were separated by at least one week to allow enough time for the drug to leave the body between visits.
Findings showed that the combination of edible cannabis and alcohol produced greater and longer-lasting effects of impaired driving and intoxication than using either substance alone, but only participants in the high alcohol dose condition (0.08% BrAC) were considered intoxicated on standard field sobriety tests compared to placebo.
“We designed this study because controlled studies have primarily focused on smoked cannabis, even though people are increasingly using edible cannabis products and alcohol together. This is the first controlled study to examine how edible cannabis and alcohol interact, despite the increased use of edible cannabis products,” said Tory Spindle, Ph.D., the study’s principal investigator and associate professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine. “Consuming common retail doses of cannabis edibles with even low doses of alcohol can result in driving impairments that are equal to or greater than the legal limit of alcohol alone.”
As cannabis legalization expands and access to cannabis products increases, researchers emphasize the importance of considering the heightened risks associated with the combination of cannabis and alcohol in public health messaging, policy, and regulatory decisions. They also note the need for continued research to better understand co-use impairment and develop improved biological or behavioral tools to detect cannabis-related impaired driving.
Other Johns Hopkins University School of Medicine faculty members who were co-investigators on this study and authors of the paper include Ryan Vandry, Ph.D., Elise Wiers, Ph.D., David Wolinsky, MD, and Denis Antoine, MD.
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Reference magazines:
Zamarripa, California; others. (2026) Effects of cannabis edibles combined with alcohol on driving, field sobriety performance, and subjective effects: A within-participant crossover study. JAMA Net Open. DOI: 10.1001/jamanetworkopen.2026.9842. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2848548
