Cannabis and Driving: New Study Examines Residual Effects on Performance

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Smoking cannabis appears to have no impairing effect on driving abilities after a period of abstinence, a recently published study demonstrated (1). Noting a lack of research in this area, researchers aimed to examine the effects of cannabis on cognition and memory in real-life situations, such as driving performance. In particular, they focused on associations between demographics, cannabis use history, and simulated driving performance after at least 48 hours of cannabis abstinence. The study, “Short-term residual effects of smoked cannabis on simulated driving performance,” was published in Psychopharmacology in September 2025. This study was split into two parts: a driving simulator with cannabis users, and a comparison between participants with the highest cannabis use and non-cannabis users.

Cannabis users and driving

This phase of the study involved 191 healthy participants, all users of cannabis to varying degrees. They completed a 25-minute simulator after at least 48 hours of abstinence from cannabis, with Composite Drive Score (CDS) used to measure driving-related variables.

Researchers found no relationship between the CDS, cannabis use history, demographics or cannabinoid content in blood samples.

Frequent Cannabis Users vs. Non-Users

Next, the researchers conducted a pilot study involving a subset of 18 of the cannabis users who had the most frequent cannabis use (smoked and at least 1 g of cannabis on 28 out of the past 30 days), and a group of 12 control participants with no cannabis use. Both groups completed driving measures with CDS tracked.

In this study, no differences were seen on CDS or driving performance between the groups.

Limitations and Next Steps for Cannabis Research

The small sample sizes for both studies was noted as one limitation to the experiment. Additionally, the data did not account for cannabis withdrawal symptoms or measure reaction time during the driving simulation. The simulation was conducted in controlled laboratory setting with a relatively simple traffic simulations, making the applications to real-world settings unclear.

Implications for Cannabis Policy and Road Safety

Overall, though, the results demonstrated no dose-dependent effects or residual short-term effects on driving performance. The researchers suggested that additional studies on short-term residual effects from cannabis smoking on driving should utilize more complex driving tasks, larger control groups, and control for confounds.

“We did not find any relationship between driving performance, and cannabis use history or time of abstinence, nor blood THC concentrations,” explained study author Kyle Mastropietro, in a press release from University of California, San Diego (2). “Of note, the most intensive users from the group, who mostly used cannabis daily and smoked an average of four joints per day, did no worse during this period of abstinence than a healthy, non-using comparison group.”

The press release added that this is the largest study of its kind to date. Additionally, the results may have implications for polices surrounding the determinations of cannabis intoxication.

“The findings add to the growing body of evidence that relying on blood THC concentrations in regular cannabis users as possible indicators of impairment is not justified, given that THC may be detectable many days (or longer) after use,” stated senior study author Thomas Marcotte, PhD, professor of psychiatry at UC San Diego School of Medicine. “The findings reinforce the challenges in relating findings from cognitive testing in very frequent users who are abstinent to how they might function during real-world, overlearned behaviors like driving.”

References

1. Mastropietro, KF., Rattigan, JA., Umlauf, A.; Grelotti, DJ.; Huestis, MA.; Suhandynata, RT.; Grant, I.; Fitzgerald, RL.; Marcotte, TD. Short-term residual effects of smoked cannabis on simulated driving performance. Psychopharmacology. 2025. DOI: 10.1007/s00213-025-06880-1
2. Martin, M. Frequent Cannabis Users Show No Driving Impairment After Two-Day Break. September 11, 2025. https://today.ucsd.edu/story/frequent-cannabis-users-show-no-driving-impairment-after-two-day-break (accessed 2025-09-23).