Does Workplace Cannabis Use Increase the Risk of Injury?

The findings come from a robust, yearly longitudinal telephone survey of 2,745 Canadian workers conducted between 2018 and 2020. Researchers investigated past-year habits, specifically separating workplace and non-workplace cannabis use.

• Workplace Consumption: Defined as cannabis use during working hours (including breaks) or within 2 hours before starting work.
• Non-Workplace Consumption: All other use outside the defined work-related window.

The study recorded that 11.3% of all workers experienced a workplace injury during the period. This figure broke down significantly by job type:

• 22.0% of workers in safety-sensitive positions reported an injury.
• 4.9% of workers in non-safety sensitive jobs reported an injury.

Notably, injuries occurring in safety-sensitive environments tended to be more severe, underscoring the higher stakes in those roles.

The core discovery of the research is stark. Analysis showed no statistically significant difference in injury risk for workers who engaged in non-workplace cannabis use compared to non-users. In dramatic contrast, workplace consumption was associated with a nearly two-fold (2X) increase in the risk of sustaining a workplace injury.

This key finding held true across different work environments. The pattern of increased risk for use at work, but not for external use, was consistent for employees in both safety-sensitive and non-safety sensitive positions. This strongly suggests the impairment effect of THC during work tasks is the primary driver of accidents, not the general status of being a consumer.

These findings carry substantial weight for employers crafting policies. They validate legitimate concerns about impairment during work hours but also challenge the scope of some existing rules.

• The data indicates that zero-tolerance policieswhich prohibit all cannabis use—including during an employee’s personal time—may be overly broad and not fully aligned with the evidence on where the actual risk lies.
• The study substantiates the need for targeted worker education programs. These should specifically highlight the risks of consuming cannabis before or during shifts.

The study’s conclusions resonate with the work of leading forensic scientists who analyze the real-world impacts of substance use. James Wigmore, one of North America’s most experienced toxicology experts, has contributed groundbreaking analysis on alcohol, cannabis (THC), and other substances over a 29-year career at Toronto’s Centre of Forensic Sciences. His expertise, spanning over 700 criminal cases, includes:

• Developing court-accepted methodologies for impairment assessment.
• Publishing definitive research on THC detection and impairment markers.
• Shaping public understanding through media commentary following legalization.

This scientific perspective underscores why distinguishing between workplace and non-workplace cannabis use is not just a policy issue, but a matter of accurate risk assessment based on forensic principles.

References

Carnide, N., Landsman, V., Lee, H., Frone, M.R., Furlan, A.D., and Smith, P.M., “Workplace and Non-Workplace Cannabis Use and the Risk of Workplace Injury” Findings from a Longitudinal Study of Canadian Workers.”, Canadian Journal of Public Health, 114: 947-955, 2023