Occasional Cannabis Users Had the Worst Driving Impairment During Distraction Tasks | Research

The takeaway

Occasional cannabis users were 3.7 times more likely to depart their lane during distracted driving after smoking, while daily users compensated by driving slower.

Cannabis users who drive, traffic safety researchers, policymakers

Occasional users: 3.71x lane departure risk

What the researchers found

Occasional cannabis users (1-2 times/week) had significantly increased lane departure risk during distraction after acute cannabis use (OR=3.71, P=0.04). Daily users did not show this increase (OR=1.56, P=0.43) but instead decreased speed relative to baseline, suggesting compensatory behavior. Changes were significantly greater for occasional vs non-use groups.

Why it matters

This challenges the assumption that all cannabis users are equally impaired. Occasional users showed the greatest safety risk, while daily users compensated, suggesting tolerance and behavioral adaptation play significant roles.

The numbers in context

85 participants (31 daily, 24 occasional, 30 non-users); occasional users OR 3.71 for lane departure; daily users OR 1.56 (ns); daily users decreased speed post-use

How the study worked

Within-subjects controlled experiment with 85 adults aged 25-45: daily users (n=31), occasional users (n=24), and non-users (n=30). Participants completed driving simulator scenarios before and 30 minutes after smoking self-procured cannabis, with distraction tasks (selecting apps on a mounted tablet).

What this study cannot tell us

Simulated driving with brief distraction tasks. Cannabis was self-procured (uncontrolled potency). Non-users did not smoke cannabis, so comparisons involve both cannabis and non-cannabis effects.

How to read the evidence

Controlled within-subjects experiment with adequate sample size, but simulated driving and self-procured cannabis limit generalizability.

When this study was published

Published in 2022

The bigger picture

Understanding that use frequency moderates driving impairment is important for policy. A one-size-fits-all approach to cannabis-impaired driving may not reflect the actual risk landscape.

Questions still open

Should impairment guidelines differentiate between occasional and daily cannabis users? Is the daily users' speed compensation sufficient to offset other impairment effects?

Common questions

Are occasional or daily cannabis users worse drivers after smoking?

Occasional users (1-2 times per week) were 3.7 times more likely to depart their lane during distracted driving, while daily users showed no significant increase and actually compensated by driving slower.

Why do daily users drive better after cannabis than occasional users?

The study suggests daily users develop both pharmacological tolerance and behavioral compensation strategies (like reducing speed). Occasional users lack these adaptations, making them more vulnerable to distraction-related errors.

Read the original research

Influence of cannabis use history on the impact of acute cannabis smoking on simulated driving performance during a distraction task.

Traffic injury prevention, 23(sup1), S1-S7

View on PubMed ↗Publisher’s paper ↗

Citation

Miller, Ryan; Brown, Tim; Wrobel, Julia; Kosnett, Michael J; Brooks-Russell, Ashley. (2022). Influence of cannabis use history on the impact of acute cannabis smoking on simulated driving performance during a distraction task.. Traffic injury prevention, 23(sup1), S1-S7. https://doi.org/10.1080/15389588.2022.2072492