Marijuana use was strongly linked to driving after drinking and riding with drunk drivers among underage drinkers | Research

The takeaway

Among underage drinkers presenting to an emergency department, past-year marijuana use more than doubled the odds of driving after drinking for females and increased it by 70% for males.

Read this if you want to understand the connection between marijuana use and impaired driving among underage drinkers.

Marijuana use: 2.3x higher odds of driving after drinking for females

What the researchers found

In a sample of 2,150 underage drinkers (ages 16-20) from an emergency department, driving after drinking (DD) was reported by 22% of females and 28% of males. Riding with a driver who had been drinking (RWDD) was reported by 39% of females and 38% of males.

Marijuana use was a strong predictor of both behaviors. For driving after drinking, marijuana use increased odds 2.3 times for females and 1.7 times for males. For riding with a drinking driver, marijuana increased odds 1.4 times for both sexes.

Prescription drug misuse was also associated with driving after drinking for both sexes and with riding with drinking drivers for females.

Why it matters

This study reveals that marijuana use is independently associated with impaired driving decisions among underage drinkers, beyond the effects of alcohol itself. The combined risk of polysubstance use and impaired driving in adolescents represents a significant public safety concern.

The numbers in context

Driving after drinking: 22% females, 28% males. Riding with drinking driver: 39% females, 38% males. Marijuana use increased DD odds: 2.3x (females), 1.7x (males). Marijuana increased RWDD odds: 1.4x (both sexes). Sample: 2,150 underage drinkers from 3,418 ED patients.

How the study worked

Cross-sectional analysis from screening data for a randomized controlled trial. 16-20 year olds (N=3,418) were surveyed in an emergency department, with analysis restricted to 2,150 who reported past-year alcohol use (58% female). Logistic regression examined associations between substance use and risky driving behaviors.

What this study cannot tell us

Cross-sectional design from an ED population, which may over-represent high-risk individuals. Self-reported behaviors may be subject to recall and social desirability bias. The study cannot determine whether marijuana use causes worse driving decisions or simply co-occurs with risk-taking personality traits. Past-year timeframe does not capture simultaneous use.

How to read the evidence

Cross-sectional analysis from an ED-based screening study. Large sample but limited by self-report and the ED setting may not represent the general adolescent population.

When this study was published

Published in 2017. Research on the intersection of marijuana use, alcohol, and driving continues as legalization expands.

The bigger picture

The co-occurrence of marijuana use, underage drinking, and impaired driving creates a cluster of risk behaviors. Addressing any one of these in isolation may miss the interconnected nature of adolescent risk-taking. ED-based interventions that address multiple substances and driving behavior simultaneously may be more effective.

Questions still open

Does marijuana impair driving judgment independently of its association with risk-taking personality? Would brief ED interventions addressing marijuana and driving together reduce impaired driving rates? How does the combined impairment from alcohol and marijuana affect crash risk compared to either substance alone?

Common questions

Does marijuana make people more likely to drive drunk?

This study found that marijuana users were more likely to drive after drinking and ride with drinking drivers. However, the cross-sectional design cannot determine causation. The association may reflect overlapping risk-taking behaviors rather than marijuana directly causing impaired driving decisions.

Why were the risks higher for females?

Females who used marijuana had 2.3 times the odds of driving after drinking compared to 1.7 times for males. The reasons are unclear but may relate to differences in social contexts of use, risk perception, or the combined effects of substances on decision-making across sexes.

Read the original research

Marijuana and other substance use among male and female underage drinkers who drive after drinking and ride with those who drive after drinking.

Addictive behaviors, 71, 7-11

View on PubMed ↗Publisher’s paper ↗

Citation

Buckley, Lisa; Bonar, Erin E; Walton, Maureen A; Carter, Patrick M; Voloshyna, Diana; Ehrlich, Peter F; Cunningham, Rebecca M. (2017). Marijuana and other substance use among male and female underage drinkers who drive after drinking and ride with those who drive after drinking.. Addictive behaviors, 71, 7-11. https://doi.org/10.1016/j.addbeh.2017.02.016