Cannabis effects on driving longitudinal control with and without alcohol.
Rebecca L Hartman, Timothy L Brown, Gary Milavetz, Andrew Spurgin, Russell S Pierce, David A. Gorelick, Gary R Gaffney, Marilyn A. Huestis
Journal of Applied Toxicology November 2016 DOI: 10.1002/jat.3295 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Within-subject experimental study Longitudinal Peer reviewed |
|---|---|
| Sample size | 18 |
| Population | Current occasional cannabis smokers (at least once in the last 3 months, no more than 3 days per week) |
| Interventions | Vaporized cannabis Alcohol |
| Dose | 500 mg placebo, low (2.9%), or high (6.7%) THC vaporized cannabis; placebo or low-dose alcohol |
| Duration | Drives 0.5-1.3 h post-inhalation; blood and breath samples at 0.17, 0.42, 1.4, and 2.3 h |
| Topics | Cannabis |
| Keywords | Alcohol Blood Driving Speed |
| Key findings | Blood THC concentration was associated with decreased mean speed, increased percent time below the speed limit, and increased following distance during headway maintenance. Breath alcohol was associated with increased speed variability and more time above the speed limit, while THC was not. The authors report a less-than-additive THC-by-alcohol interaction on speeding, suggesting cannabis mitigated drivers' tendency to drive faster with alcohol. |
Abstract
Although evidence suggests cannabis impairs driving, its driving-performance effects are not fully characterized. We aimed to establish cannabis' effects on driving longitudinal control (with and without alcohol, drivers' most common drug combination) relative to psychoactive ∆(9) -tetrahydrocannabinol (THC) blood concentrations. Current occasional (≥1×/last 3 months, ≤3 days per week) cannabis smokers drank placebo or low-dose alcohol, and inhaled 500 mg placebo, low (2.9%), or high (6.7%) THC vaporized cannabis over 10 min ad libitum in separate sessions (within-subject, six conditions). Participants drove (National Advanced Driving Simulator, University of Iowa) simulated drives 0.5-1.3 h post-inhalation. Blood and breath alcohol samples were collected before (0.17 and 0.42 h) and after (1.4 and 2.3 h) driving. We evaluated the mean speed (relative to limit), standard deviation (SD) of speed, percent time spent >10% above/below the speed limit (percent speed high/percent speed low), longitudinal acceleration, and ability to maintain headway relative to a lead vehicle (headway maintenance) against blood THC and breath alcohol concentrations (BrAC). In N=18 completing drivers, THC was associated with a decreased mean speed, increased percent speed low and increased mean following distance during headway maintenance. BrAC was associated with increased SD speed and increased percent speed high, whereas THC was not. Neither was associated with altered longitudinal acceleration. A less-than-additive THC*BrAC interaction was detected in percent speed high (considering only non-zero data and excluding an outlying drive event), suggesting cannabis mitigated drivers' tendency to drive faster with alcohol. Cannabis was associated with slower driving and greater headway, suggesting a possible awareness of impairment and attempt to compensate. Copyright © 2016 John Wiley & Sons, Ltd.
Comparable studies
Other experimental studies on cannabis, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| Smoked Cannabis' Psychomotor and Neurocognitive Effects in Occasional and Frequent Smokers Occasional (<2x/week) and frequent (≥4x/week) cannabis smokers | 2015 | Controlled within-subjects study | n = 25 |
| Dissociable effects of cannabis with and without cannabidiol on the human brain’s resting-state functional connectivity Healthy volunteers experienced with cannabis but not regular users | 2019 | Within-subjects experimental design | n = 17 |
| Which biological and self-report measures of cannabis use predict cannabis dependency and acute psychotic-like effects? Young cannabis users | 2018 | Observational study (naturalistic, within-subject counterbalanced design) | n = 410 |
| Cannabis Essential Oil: A Preliminary Study for the Evaluation of the Brain Effects Healthy volunteers | 2018 | Experimental study | n = 5 |
| Coming off cannabis: a cognitive and magnetic resonance imaging study in patients with multiple sclerosis Patients with multiple sclerosis who began using cannabis after disease onset, used it... | 2019 | Quasi-experimental study with odd-even allocation | n = 40 |
Citations in the library
Cited by 5
- Cannabidiol (CBD) content in vaporized cannabis does not prevent tetrahydrocannabinol (THC)-induced impairment of driving and cognition Psychopharmacology May 1, 2019
- The effect of cannabis edibles on driving and blood THC. Journal of Cannabis Research May 31, 2024
- Cognitive performance recovery following marijuana cessation in NCAA division I athletes. Frontiers in Sports and Active Living 2026
- Self-Regulation of Driving Behavior Under the Influence of Cannabis: The Role of Driving Complexity and Driver Vision. Human factors November 2023
- Perceived effects of cannabis: Generalizability of changes in driving performance. Traffic injury prevention 2022
Cites 5
- Tolerance and cross-tolerance to neurocognitive effects of THC and alcohol in heavy cannabis users Psychopharmacology October 30, 2010
- Smoked Cannabis' Psychomotor and Neurocognitive Effects in Occasional and Frequent Smokers Journal of Analytical Toxicology March 4, 2015
- The effect of alcohol, THC and their combination on perceived effects, willingness to drive and performance of driving and non-driving tasks. Accident; Analysis and Prevention November 2010
- Neurocognitive performance during acute THC intoxication in heavy and occasional cannabis users. Journal of Psychopharmacology May 2009
- Effects of THC on driving performance, physiological state and subjective feelings relative to alcohol. Accident; Analysis and Prevention May 2008