Heavy recreational cannabis users showed impaired driving even when not high, especially those who started before age 16
Non-intoxicated heavy recreational cannabis users demonstrated impaired driving simulator performance compared to controls, with impairment entirely localized to those who began regular use before age 16.
Quick Facts
What This Study Found
Cannabis users showed increased accidents, speed, lateral movement, and reduced rule-following compared to controls. When divided by onset age, all significant driving impairment was localized to early-onset users (before age 16). Late-onset users (16+) did not differ significantly from controls. Impulsivity significantly contributed to performance differences.
Key Numbers
Cannabis users had increased accidents, speed, lateral movement, and reduced rule-following. All impairment localized to early-onset (<16) group. Late-onset (16+) group did not differ from controls. Impulsivity was a significant covariate.
How They Did This
Cross-sectional study comparing non-intoxicated heavy recreational cannabis users with healthy controls on a customized driving simulator. Users divided into early-onset (<16) and late-onset (16+) groups. Impulsivity assessed as a covariate.
Why This Research Matters
This suggests chronic cannabis use may impair driving ability even when users are not actively intoxicated, with age of first regular use being a critical factor.
The Bigger Picture
The finding that only early-onset users showed persistent driving impairment reinforces concerns about adolescent cannabis use and its potential for lasting neurocognitive effects on complex real-world tasks.
What This Study Doesn't Tell Us
Cross-sectional design; simulated driving not identical to real driving; cannot determine if early-onset users had pre-existing differences that led to both earlier use and poorer driving; relatively small sample.
Questions This Raises
- ?Is the early-onset driving impairment caused by cannabis effects on brain development, or does impulsivity drive both early use and poor driving?
- ?Would driving impairment resolve with sustained abstinence?
Trust & Context
- Key Stat:
- All driving impairment was localized to those who started regular use before age 16
- Evidence Grade:
- Cross-sectional with simulated driving; cannot determine causation or separate cannabis effects from pre-existing traits.
- Study Age:
- Published in 2020.
- Original Title:
- Recreational cannabis use impairs driving performance in the absence of acute intoxication.
- Published In:
- Drug and alcohol dependence, 208, 107771 (2020)
- Authors:
- Dahlgren, M Kathryn(2), Sagar, Kelly A(7), Smith, Rosemary T(6), Lambros, Ashley M, Kuppe, Madeline K, Gruber, Staci A
- Database ID:
- RTHC-02491
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Can sober cannabis users still be impaired drivers?
This study found heavy recreational users showed impaired simulated driving even when not intoxicated, but only among those who started regular use before age 16. Those who started at 16 or later performed similarly to non-users.
Why does age of first use matter for driving?
The brain is still developing during adolescence. Starting regular cannabis use before 16 may affect brain regions involved in impulse control, attention, and decision-making that are critical for driving. However, the study cannot fully separate cannabis effects from pre-existing impulsivity.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-02491APA
Dahlgren, M Kathryn; Sagar, Kelly A; Smith, Rosemary T; Lambros, Ashley M; Kuppe, Madeline K; Gruber, Staci A. (2020). Recreational cannabis use impairs driving performance in the absence of acute intoxication.. Drug and alcohol dependence, 208, 107771. https://doi.org/10.1016/j.drugalcdep.2019.107771
MLA
Dahlgren, M Kathryn, et al. "Recreational cannabis use impairs driving performance in the absence of acute intoxication.." Drug and alcohol dependence, 2020. https://doi.org/10.1016/j.drugalcdep.2019.107771
RethinkTHC
RethinkTHC Research Database. "Recreational cannabis use impairs driving performance in the..." RTHC-02491. Retrieved from https://rethinkthc.com/research/dahlgren-2020-recreational-cannabis-use-impairs
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.