Older Drivers and THC: A Meta-Analysis Found Null Associations With Important Uncertainty
A 2023 meta-analysis did not find statistically significant associations between THC exposure and either collision involvement or collision culpability among drivers aged 50 and older. Its confidence intervals and study designs prevent interpreting that result as proof of no risk.
Two outcomes were analyzed separately
The review included seven cross-sectional studies: four examined collisions and three examined culpability. Being involved in a collision and being assessed as responsible are different outcomes. A combined statement about cannabis-related crashes should preserve that distinction.
The estimates retained uncertainty
The pooled collision odds ratio was 1.15, with a 95% confidence interval of 0.40–3.31. The culpability estimate was 1.24, with an interval of 0.95–1.61. Both intervals included the null value. The collision estimate was especially imprecise and heterogeneous; lack of statistical significance does not demonstrate equivalence.
Exposure classification is not a functional test
The comparison concerned THC exposure or positivity as defined by the underlying studies. It was not a controlled determination of each driver's impairment at a specified dose. Cross-sectional evidence also leaves important questions about timing, co-exposures and selection of the studied drivers.
Interpreting the evidence
The appropriate conclusion is a non-significant pooled association in this older-driver evidence base, with uncertainty preserved. It does not establish safe cannabis-impaired driving, exclude a meaningful association or resolve whether an individual driver was impaired.
Related reading: interpreting cannabis tolerance claims.
Research reference
Arun Chinna-Meyyappan; Hui Jue Wang; Kritleen K. Bawa; Edward Ellazar; Emilie Norris-Roozmon; Gary Naglie; Nathan Herrmann; Judith L. Charlton; Sjaan Koppel; Saulo Castel; Krista L. Lanctôt; Mark J. Rapoport (2023). Risk of Motor Vehicle Collisions and Culpability among Older Drivers Using Cannabis: A Meta-Analysis. Brain Sciences. doi:10.3390/brainsci13030421.
This analysis draws on the supplied review’s abstract and introductory material.
