What Research Shows About How Cannabis Affects Driving Ability
A comprehensive review found that cannabis impairs driving by increasing lane weaving and following distance, with cognitive deficits extending weeks after cessation, and combined alcohol-cannabis use producing greater impairment than either alone.
Quick Facts
What This Study Found
This review synthesized evidence from laboratory, simulator, on-road, and brain imaging studies to assess how cannabis affects driving performance.
Cannabis impaired actual driving by increasing lane weaving and the mean distance to the vehicle ahead. Specific cognitive functions and psychomotor abilities showed acute and long-term dose-dependent impairments that extended beyond several weeks after stopping use.
Combined use of alcohol and cannabis produced greater odds of driving errors than either substance alone. Blood sampling was identified as the most effective method for evaluating driver impairment, and blood tests could also identify chronic use suggesting long-term unfitness to drive. Some inconsistencies between studies were attributed to differences in cannabis use history, route of administration, dose, and study design.
Key Numbers
Cannabis increased lane weaving and mean headway distance in on-road studies. Cognitive impairments extended beyond several weeks after cessation. Combined alcohol-cannabis use increased error rates beyond either substance alone.
How They Did This
This was a comprehensive review examining laboratory studies, driving simulator studies, on-road driving studies, and structural and functional brain imaging research on cannabis and driving performance.
Why This Research Matters
As cannabis legalization expands, understanding its effects on driving becomes a public safety priority. This review consolidates evidence showing that cannabis impairs driving performance through multiple mechanisms, and that the effects can persist well beyond the period of acute intoxication.
The Bigger Picture
The review highlights a key challenge in cannabis-impaired driving: unlike alcohol, blood THC levels do not correlate well with actual impairment. This makes enforcement more difficult and continues to drive research into better methods for assessing cannabis-related driving impairment.
What This Study Doesn't Tell Us
Discrepancies between studies were noted, partly due to differences in participant cannabis use history, tolerance development, and study methodology. The correlation between blood THC levels and actual impairment remains poorly understood. Most studies used controlled laboratory or simulator settings rather than real-world driving.
Questions This Raises
- ?How long after cannabis use is it safe to drive?
- ?Can better biomarkers for cannabis-related driving impairment be developed?
Trust & Context
- Key Stat:
- Cognitive driving impairments extended beyond several weeks after cannabis cessation
- Evidence Grade:
- This is a comprehensive review drawing on multiple study types including on-road driving research, providing moderate-quality evidence on cannabis-driving effects.
- Study Age:
- Published in 2016. Research on cannabis and driving has continued, though the fundamental challenge of correlating blood levels with impairment persists.
- Original Title:
- Cannabis and its effects on driving skills.
- Published In:
- Forensic science international, 268, 92-102 (2016)
- Authors:
- Bondallaz, Percy, Favrat, Bernard(3), Chtioui, Haïthem, Fornari, Eleonora, Maeder, Philippe, Giroud, Christian
- Database ID:
- RTHC-01109
Evidence Hierarchy
Summarizes existing research on a topic.
What do these levels mean? →Frequently Asked Questions
How long do cannabis effects on driving last?
This review found that cognitive and psychomotor impairments relevant to driving extended beyond several weeks after stopping cannabis use. The acute effects are strongest in the first few hours, but regular users may have lingering deficits.
Is driving on cannabis as dangerous as driving drunk?
The review found that cannabis impairs driving performance but in different ways than alcohol. Combined use of both substances produces greater impairment than either alone. Direct comparison of danger levels is complicated by differences in how each substance affects driving behavior.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-01109APA
Bondallaz, Percy; Favrat, Bernard; Chtioui, Haïthem; Fornari, Eleonora; Maeder, Philippe; Giroud, Christian. (2016). Cannabis and its effects on driving skills.. Forensic science international, 268, 92-102. https://doi.org/10.1016/j.forsciint.2016.09.007
MLA
Bondallaz, Percy, et al. "Cannabis and its effects on driving skills.." Forensic science international, 2016. https://doi.org/10.1016/j.forsciint.2016.09.007
RethinkTHC
RethinkTHC Research Database. "Cannabis and its effects on driving skills." RTHC-01109. Retrieved from https://rethinkthc.com/research/bondallaz-2016-cannabis-and-its-effects
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.