In Uruguay, the number of registered cannabis self-cultivators was significantly associated with more traffic crashes involving injuries, while overall cannabis registrations and other supply mechanisms showed no consistent association.
Policymakers designing legal cannabis supply systems, traffic safety researchers, and regulators evaluating home cultivation rules.
Self-cultivation linked to crashes; pharmacy purchases not
What the researchers found
Total cannabis registrations were not associated with traffic crashes. However, self-cultivation registrations showed a consistent, positive, and statistically significant association with traffic crashes involving injuries (beta = 0.194, p = 0.008). Associations for pharmacy purchasing and cannabis club membership were inconsistent across model specifications.
Why it matters
How a country structures its legal cannabis supply may matter for traffic safety. Uruguay's unique three-pathway system allows this comparison, and the finding that self-cultivation specifically is associated with crashes suggests supply mechanism design matters.
The numbers in context
Average registrations per 10,000 adults: self-cultivation 17.7, clubs 3.6, pharmacies 25.1. Self-cultivation and crashes: beta = 0.194, p = 0.008, 95% CI 0.058-0.329. Total registrations: beta = -0.007, p = 0.398 (not significant).
How the study worked
Ecological study using ordinary least squares regression with department-level quarterly data from Uruguay (2013-2019). Cannabis registration counts by supply type (self-cultivation, clubs, pharmacies) were examined against traffic crash data, controlling for economic and demographic characteristics.
What this study cannot tell us
Ecological study cannot establish individual-level causation. Self-cultivators may differ from pharmacy purchasers in unmeasured ways. Traffic crash data may not capture all incidents. Cannot determine whether self-cultivators themselves are crashing or if the association reflects broader community effects.
How to read the evidence
Ecological study with appropriate controls but unable to establish individual-level causation.
When this study was published
Published in 2022, covering 2013-2019.
The bigger picture
This is the first study to examine how different legal cannabis supply mechanisms relate to traffic safety. If self-cultivation carries unique risks, it may be because of less quality control, different consumption patterns, or characteristics of people who choose this option.
Questions still open
- Are self-cultivators using more potent cannabis? Do self-cultivators have different consumption patterns that increase driving risk? Would regulating homegrown potency address this association?
Common questions
Does legal cannabis increase car crashes?
Does it matter where people get their legal cannabis?
Read the original research
Cannabis legalization and traffic injuries: exploring the role of supply mechanisms.
Addiction (Abingdon, England), 117(8), 2325-2330
Citation
Kilmer, Beau; Rivera-Aguirre, Ariadne; Queirolo, Rosario; Ramirez, Jessica; Cerdá, Magdalena. (2022). Cannabis legalization and traffic injuries: exploring the role of supply mechanisms.. Addiction (Abingdon, England), 117(8), 2325-2330. https://doi.org/10.1111/add.15840