Using Alcohol and Cannabis Together Changes How People Judge Their Driving Ability
In 88 adults who regularly co-use alcohol and cannabis, simultaneous use increased perceived driving impairment but paradoxically also increased willingness to drive compared to alcohol alone.
Quick Facts
What This Study Found
Simultaneous alcohol and cannabis use increased perceived driving impairment, yet participants were 3.7x more willing to drive within an hour compared to alcohol-only use, suggesting cannabis may attenuate alcohol's deterrent effect on driving decisions.
Key Numbers
88 adults, 14 days of EMA, average 5.14 surveys/day. Simultaneous users were 3.69x more willing to drive within 1 hour (95% CI: 2.15-6.34) compared to alcohol-only use.
How They Did This
Ecological momentary assessment over 14 days with 88 adults (ages 18-44) who co-use alcohol and cannabis at least twice weekly, completing an average of 5.14 surveys per day on substance use, perceived impairment, and driving willingness.
Why This Research Matters
People who use alcohol and cannabis together are at higher crash risk, yet this study suggests they may actually feel more willing to drive — a dangerous mismatch between impairment and risk perception.
The Bigger Picture
As cannabis legalization expands, simultaneous use with alcohol is increasing. Understanding how this combination affects driving decisions — not just driving ability — is critical for public safety messaging.
What This Study Doesn't Tell Us
Self-selected sample of regular co-users may not represent broader population. Self-reported willingness to drive differs from actual driving behavior. Predominantly White sample (85.2%) limits diversity.
Questions This Raises
- ?Does cannabis create a false sense of sobriety when combined with alcohol?
- ?Should impaired driving campaigns specifically address simultaneous use scenarios?
Trust & Context
- Key Stat:
- Evidence Grade:
- Innovative real-time EMA methodology capturing in-the-moment decisions, though limited by self-report and specific population.
- Study Age:
- Recent study using ecological momentary assessment to capture real-world driving decisions during substance use.
- Original Title:
- Event-level influences of alcohol, cannabis, and simultaneous use on perceived driving risk.
- Published In:
- Experimental and clinical psychopharmacology, 33(2), 170-177 (2025)
- Authors:
- Wycoff, Andrea M(2), Darmour, Charles A, McCarthy, Denis M(3), Trull, Timothy J
- Database ID:
- RTHC-07980
Evidence Hierarchy
Watches what happens naturally without intervening.
What do these levels mean? →Frequently Asked Questions
Is it more dangerous to drive after using both alcohol and cannabis?
Yes — lab studies show simultaneous use impairs driving more than either substance alone. This study adds that people may paradoxically feel more willing to drive despite greater impairment.
Why would cannabis make people more willing to drive after drinking?
The authors suggest cannabis may attenuate alcohol's subjective effects on driving decision-making, creating a dangerous disconnect between actual impairment and perceived ability to drive.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-07980APA
Wycoff, Andrea M; Darmour, Charles A; McCarthy, Denis M; Trull, Timothy J. (2025). Event-level influences of alcohol, cannabis, and simultaneous use on perceived driving risk.. Experimental and clinical psychopharmacology, 33(2), 170-177. https://doi.org/10.1037/pha0000758
MLA
Wycoff, Andrea M, et al. "Event-level influences of alcohol, cannabis, and simultaneous use on perceived driving risk.." Experimental and clinical psychopharmacology, 2025. https://doi.org/10.1037/pha0000758
RethinkTHC
RethinkTHC Research Database. "Event-level influences of alcohol, cannabis, and simultaneou..." RTHC-07980. Retrieved from https://rethinkthc.com/research/wycoff-2025-eventlevel-influences-of-alcohol
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.