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.
Public safety researchers, impaired driving prevention advocates, and people who use alcohol and cannabis together.
What the researchers 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.
Why it 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 numbers in context
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 the study worked
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.
What this study cannot 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.
How to read the evidence
Innovative real-time EMA methodology capturing in-the-moment decisions, though limited by self-report and specific population.
When this study was published
Recent study using ecological momentary assessment to capture real-world driving decisions during substance use.
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.
Questions still open
- Does cannabis create a false sense of sobriety when combined with alcohol? Should impaired driving campaigns specifically address simultaneous use scenarios?
Common questions
Is it more dangerous to drive after using both alcohol and cannabis?
Why would cannabis make people more willing to drive after drinking?
Read the original research
Event-level influences of alcohol, cannabis, and simultaneous use on perceived driving risk.
Experimental and clinical psychopharmacology, 33(2), 170-177
Citation
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