Among 367 college drinkers, those who also used marijuana and nicotine had over 10 times the odds of driving under the influence and riding with an impaired driver compared to alcohol-only users.
College health professionals, impaired driving prevention researchers, and substance use educators.
10x higher DUI odds when all three substances were used together
What the researchers found
Compared to alcohol-only users, students using all three substances (alcohol, marijuana, nicotine) had dramatically higher odds of DUI (OR=10.33) and riding with an impaired driver (OR=10.22). Marijuana-only users also had elevated DUI risk (OR=5.44 between-person; OR=9.08 on specific occasions). On days when both alcohol and marijuana were used, riding with an impaired driver was nearly 4 times more likely (OR=3.86).
Why it matters
Prevention programs typically focus on alcohol-impaired driving. This study shows that polysubstance use dramatically increases driving risk beyond alcohol alone, suggesting prevention efforts need to address substance combinations rather than single substances.
The numbers in context
367 students. All three substances vs. alcohol only: DUI OR=10.33, RWID OR=10.22. Marijuana-only users vs. alcohol-only: DUI OR=5.44. Marijuana-only occasions vs. alcohol-only occasions: DUI OR=9.08. Alcohol+marijuana occasions: RWID OR=3.86. Confidence intervals were wide.
How the study worked
Burst design study of 367 college student drinkers with past-year marijuana and/or nicotine use. Assessed on two consecutive weekends for three semesters. Logistic and multilevel logistic models examined between- and within-person associations of substance combinations with DUI and RWID.
What this study cannot tell us
Wide confidence intervals reflect small cell sizes for some substance combinations. Self-reported substance use and driving behavior. College student sample limits generalizability. Cannot determine impairment level at time of driving.
How to read the evidence
Longitudinal burst design captures within-person effects, but wide confidence intervals and self-reported measures are limitations.
When this study was published
2021 study with data from a Midwestern university.
The bigger picture
The finding that marijuana-only occasions carried high DUI risk (OR=9.08) is notable because cannabis-impaired driving receives less attention than alcohol-impaired driving. The multiplicative risk of combining all three substances underscores that polysubstance use creates qualitatively different risk profiles.
Questions still open
- Why does nicotine add to DUI risk beyond alcohol and marijuana? Are polysubstance users also engaging in heavier use of each substance? Would campus-level interventions targeting polysubstance use reduce impaired driving?
Common questions
Did marijuana alone increase DUI risk?
Why were the odds ratios so large?
Read the original research
Alcohol, marijuana, and nicotine use as predictors of impaired driving and riding with an impaired driver among college students who engage in polysubstance use.
Accident; analysis and prevention, 160, 106341
Citation
Hultgren, Brittney A; Waldron, Katja A; Mallett, Kimberly A; Turrisi, Rob. (2021). Alcohol, marijuana, and nicotine use as predictors of impaired driving and riding with an impaired driver among college students who engage in polysubstance use.. Accident; analysis and prevention, 160, 106341. https://doi.org/10.1016/j.aap.2021.106341