Table of Contents
Clinical Takeaway
Combining cannabis edibles with alcohol produces greater driving impairment than either substance alone, based on controlled crossover trial data. Both substances independently worsened simulated driving performance and field sobriety measures, with co-use amplifying these effects. Patients should be clearly counseled that using cannabis edibles alongside alcohol significantly increases impairment risk, including for driving.
#7 Impact of Cannabis Edibles Combined With Alcohol on Driving, Field Sobriety Performance, and Subjective Effects: A Within-Participant Crossover Trial.
Citation: Zamarripa C Austin et al.. Impact of Cannabis Edibles Combined With Alcohol on Driving, Field Sobriety Performance, and Subjective Effects: A Within-Participant Crossover Trial.. JAMA network open. 2026. PMID: 42065887.
Design: 5 Journal: 4 N: 0 Recency: 3 Pop: 1 Human: 1 Risk: -2
- Preclinical only
Abstract: IMPORTANCE: Simultaneous cannabis and alcohol use (co-use) is a public safety concern. Controlled data on the effects of co-ingestion of oral cannabis products (edibles) with alcohol are lacking, despite an increased prevalence of this behavior. OBJECTIVE: To evaluate the individual and interactive effects of cannabis edibles and alcohol on simulated driving and subjective and objective impairment measures. DESIGN, SETTING, AND PARTICIPANTS: This within-participant, double-blind, double-dummy crossover study of healthy adults included 7 outpatient sessions, separated by 1 week, at Johns Hopkins University School of Medicine from February 2022 to August 2025. INTERVENTION: Brownies containing 0 mg, 10 mg, or 25 mg ฮ9-tetrahydrocannabinol (THC) combined with placebo drinks or alcohol-containing drinks, calculated to achieve breath alcohol concentrations (BrACs) of 0%, 0.05%, or 0.08%. MAIN OUTCOMES AND MEASURES: Driving outcomes included the global drive score (GDS), a composite index of multiple driving measures, and the standard deviation of lateral position as the main outcomes. Other outcomes included cumulative impairment clues on standardized field sobriety tests (SFSTs), subjective drug effects, cognitive and psychomotor performance (using the DRUID [Driving Under the Influence of Drugs] application), and blood cannabinoid concentrations. RESULTS: Participants included 25 healthy adults (15 males [60%]; mean [SD] age, 25.6 [4.9] years) who reported recent binge drinking, prior cannabis and alcohol co-use, and fewer than 3 cannabis uses per week. Compared with placebo, all active drug conditions except 10 mg THC negatively impacted driving performance (ie, GDS). Driving impairment from alcohol alone at 0.08% BrAC was comparable with that of 0.05% BrAC and 10 mg THC (mean [SD] GDS, 1.6 [1.6] vs 1.6 [1.4]) and significantly lower than 0.05% BrAC and 25 mg THC (mean [SD] GDS, 2.5 [1.7]; Pโ=โ.02). Driving impairment and subjective intoxication (eg, confidence to dri
What This Study Teaches Us
Cannabis edibles and alcohol produce measurable impairment on simulated driving tests, with most active drug combinations (except 10 mg THC alone) worsening performance compared to placebo. The impairment from 0.08% breath alcohol was comparable to that from 10 mg THC, suggesting both substances carry meaningful driving risk at these doses.
Why This Matters Clinically
Co-use of cannabis edibles and alcohol is increasingly common, but we’ve had almost no controlled human data on how they interact during driving. Clinicians counseling patients about cannabis, alcohol, or both need concrete information to discuss real-world safety, and this study provides the first rigorous evidence in a driving simulator.
Study Snapshot
| Study Design | Within-participant double-blind double-dummy crossover trial with 7 sessions separated by 1 week |
| Population | 25 healthy adults (60% male, mean age 25.6 years) with recent binge drinking, prior cannabis-alcohol co-use, and less than 3 cannabis uses per week |
| Intervention | THC edibles (brownies containing 0, 10, or 25 mg THC) combined with placebo or alcohol drinks targeting breath alcohol concentrations of 0%, 0.05%, or 0.08% |
| Primary Outcome | Global drive score (composite index of multiple driving measures) and standard deviation of lateral position on simulated driving task |
| Key Result | All active drug conditions except 10 mg THC alone impaired driving performance; 0.08% BAC impairment was comparable to 10 mg THC impairment |
Where This Paper Deserves Skepticism
The sample is small (N=25) and restricted to young adults with recent binge drinking and prior co-use experience, so findings may not generalize to older users, infrequent users, or those without a history of combined use. A simulated driving test measures only intermediate performance outcomes, not crash risk in real traffic. The abstract cuts off mid-sentence on a key comparison, making it impossible to assess the full interaction effects or whether certain combinations showed synergistic impairment. Funding source is not mentioned in the abstract.
Dr. Caplan’s Take
This is the kind of study we’ve been missing. The controlled setting at Johns Hopkins with blinded dosing gives us real signal on a behavior that’s already happening in the real world. What I take from this: a single 10 mg THC edible appears to produce less driving impairment than we might have expected, but 25 mg does not, and the interaction with alcohol matters. I’m cautious about over-interpreting the 10 mg finding in isolation because sample size is modest and individual variation is real, but the overall message is sound: combining these substances merits explicit patient counseling.
Clinical Bottom Line
In this controlled trial, cannabis edibles at 25 mg THC and most combinations with alcohol measurably impaired simulated driving, with effects comparable to legal intoxication thresholds. Clinicians should advise patients that co-use carries documented driving risk and counsel against driving after combined cannabis and alcohol use.
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