Acute THC use slows and impairs eye movement control, while chronic users show lasting deficits in visual scanning.
Traffic safety researchers, law enforcement developing impairment testing, and policymakers addressing drugged driving.
Acute THC slows eye movements and impairs inhibitory control; chronic users show lasting deficits
What the researchers found
Across 20 studies, acute THC consumption increased saccadic latency, reduced accuracy, and impaired inhibitory control. Chronic cannabis users, particularly those who started young, showed enduring oculomotor deficits affecting visual scanning efficiency. Eyelid tremors appeared to be a reliable indicator of cannabis consumption but were distinct from impairment.
Why it matters
Current roadside cannabis tests detect THC but do not measure actual impairment. Identifying specific eye movement changes could lead to more accurate, impairment-based testing.
The numbers in context
20 studies included (12 acute dosing, 5 chronic use, 3 roadside). Acute THC increased saccadic latency and inaccuracy. Chronic users with early onset showed lasting oculomotor deficits.
How the study worked
Systematic review registered on OSF following PRISMA guidelines. Twenty articles included: 12 acute dosing trials, 5 chronic use cross-sectional studies, and 3 roadside epidemiological studies.
What this study cannot tell us
Heterogeneous study designs and THC doses limit direct comparison. Most acute studies used controlled lab settings that may not reflect real-world driving.
How to read the evidence
Systematic review with pre-registration and PRISMA reporting, though included studies varied in design and THC dosing.
When this study was published
Published in 2024.
The bigger picture
As cannabis legalization spreads, the gap between detecting consumption and proving impairment becomes a legal and safety issue. Eye movement testing could bridge this gap.
Questions still open
- Could an eye-tracking device provide a standardized, objective roadside impairment test for cannabis?
- Do oculomotor deficits in chronic users recover after extended abstinence?
Common questions
Can eye tests detect cannabis impairment?
Do long-term cannabis users have permanent eye movement problems?
Read the original research
A systematic review of oculomotor deficits associated with acute and chronic cannabis use.
Addiction biology, 29(1), e13359
Citation
Manning, Brooke; Downey, Luke A; Narayan, Andrea; Hayley, Amie C. (2024). A systematic review of oculomotor deficits associated with acute and chronic cannabis use.. Addiction biology, 29(1), e13359. https://doi.org/10.1111/adb.13359