Determining the magnitude and duration of acute Δ9-tetrahydrocannabinol (Δ9-THC)-induced driving and cognitive impairment: A systematic and meta-analytic review.
D. McCartney, Thomas R. Arkell, Christopher Irwin, I. McGregor
Neuroscience and biobehavioral reviews January 23, 2021 DOI: 10.1016/j.neubiorev.2021.01.003 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Systematic review Peer reviewed |
|---|---|
| Dose | 20 mg of Δ9-THC (inhaled) |
| Topics | Cannabis |
| Key findings | Meta-analyses found that peak Δ9-THC effects impaired driving performance and driving-related cognitive skills such as lateral control, tracking, and divided attention. Regular cannabis users showed less impairment than occasional users, and impairment magnitude depended on dose, time since use, and the skill assessed. A model predicted impairment would take about 7 hours to subside after inhaling 20 mg of Δ9-THC, with oral use possibly taking longer; the authors suggest waiting at least 7 hours after inhaled cannabis before safety-sensitive tasks. |
Abstract
The increasing legal availability of cannabis has important implications for road safety. This systematic review characterised the acute effects of Δ9-THC on driving performance and driving-related cognitive skills, with a particular focus on the duration of Δ9-THC-induced impairment. Eighty publications and 1534 outcomes were reviewed. Several measures of driving performance and driving-related cognitive skills (e.g. lateral control, tracking, divided attention) demonstrated impairment in meta-analyses of "peak" Δ9-THC effects (p's<0.05). Multiple meta-regression analyses further found that regular cannabis use was associated with less impairment than 'other' (mostly occasional) cannabis use (p = 0.003) and that the magnitude of oral (n = 243 effect estimates [EE]) and inhaled (n = 481 EEs) Δ9-THC-induced impairment depended on various factors (dose, post-treatment time interval, the performance domain (skill) assessed) in other cannabis users (p's<0.05). The latter model predicted impairment would take ∼7 -hs to subside (Hedges' g=-0.25) after inhaling 20 mg of Δ9-THC; oral Δ9-THC-induced impairment may take longer to subside. These results suggest individuals should wait at least 7 -hs following inhaled cannabis use before performing safety-sensitive tasks.
Comparable studies
Other systematic reviews and meta-analyses on cannabis, most cited first.
| Study | Year | Design | Participants |
|---|---|---|---|
| Effects of cannabis use on outcomes of psychotic disorders: systematic review People with psychotic disorders, as examined in 13 longitudinal studies | 2008 | Systematic review | |
| The Impact of Cannabis Use on Cognitive Functioning in Patients With Schizophrenia: A Meta-analysis of Existing Findings and New Data in a First-Episode Sample Patients with established schizophrenia (meta-analysis: 572) and patients with... | 2010 | Meta-analysis and cross-sectional observational study | n = 700 |
| Medicinal cannabis for psychiatric disorders: a clinically-focused systematic review | 2020 | Systematic review | |
| Neuroimaging in cannabis use: a systematic review of the literature Cannabis users and controls in neuroimaging studies | 2009 | Systematic review | |
| Human Laboratory Studies on Cannabinoids and Psychosis. Healthy human subjects and individuals with schizophrenia | 2016 | Systematic review |
Citations in the library
Cited by 22
- Challenges and considerations for treating PTSD with medicinal cannabis: the Australian clinician's perspective. Expert Review of Clinical Pharmacology 2023
- Sex differences in the acute effects of cannabis on human cognition: A systematic review. Frontiers in neuroendocrinology October 1, 2025
- Randomized Laboratory Study of Single-Dose Cannabis, Dronabinol, and Placebo in Patients With Schizophrenia and Cannabis Use Disorder Schizophrenia Bulletin June 20, 2024
- Caffeine, nicotine, cannabis, and psilocybin: Pharmacology, toxicology, and potential therapeutic uses of four naturally occurring psychoactive substances Swiss Medical Weekly July 1, 2025
- Effects of naturalistic doses of cannabis edibles on cognition and association with blood THC. Psychopharmacology March 1, 2026
and 17 more in the library
Cites 18
- Cannabidiol (CBD) content in vaporized cannabis does not prevent tetrahydrocannabinol (THC)-induced impairment of driving and cognition Psychopharmacology May 1, 2019
- Cannabis and tolerance: acute drug impairment as a function of cannabis use history Scientific Reports May 26, 2016
- Cannabis smoking impairs driving performance on the simulator and real driving: a randomized, double‐blind, placebo‐controlled, crossover trial Fundamental and Clinical Pharmacology May 12, 2018
- Reduced responsiveness of the reward system is associated with tolerance to cannabis impairment in chronic users Addiction Biology December 22, 2019
- Single doses of THC and cocaine decrease proficiency of impulse control in heavy cannabis users British Journal of Pharmacology October 11, 2013
and 13 more in the library