Cannabis in the workplace

Workers who consume cannabis off the clock are no more likely to be victims of workplace accidents than non-cannabis consumers. This is according to a new study published in the Canadian Journal of Public Health.

The longitudinal study of Canadian workers appears to have debunked zero-tolerance policies. It may also challenge jobs that require drug tests.

However, the researchers found that those who consume cannabis during work hours are nearly twice as likely to be involved in a workplace accident.

Details of the Cannabis-in-the-Workplace Study

Details of the Cannabis-in-the-Workplace Study

This cannabis-in-the-workplace study followed 2,745 Canadian workers. Some of the participants were employed in safety-sensitive positions. Researchers followed the workers for two years, with 11.3 percent of their sample experiencing workplace injuries.

According to researchers, 10.2 percent of those hurt on the job fell into the non-consumer category. 11.14 percent were consumers who partook at home, off work hours.

Those who consumed cannabis during work (or two hours before) were 20.13 percent more likely to be involved in a workplace accident.

“Compared to no past-year use, the risk of experiencing a workplace injury was 1.97 times higher among workers reporting workplace use,” the study says. “No statistically elevated association was seen for non-workplace use.”

“Results of this novel study suggest workplace cannabis use, not use outside of work, is a risk factor for workplace injuries,” the authors concluded.

This cannabis-in-the-workplace study contradicts earlier findings that supported the notion that cannabis consumers are more likely to be involved in an accident.

The reason for this, write the researchers, is the time factor.

“Findings suggest that, when thinking about the potential occupational safety impacts of a worker’s cannabis use, it is important to consider when that use is taking place,” the authors write. “More specifically, only use in close temporal proximity to work appears to be a risk factor for workplace injuries, not use away from work.”

Concluding, “zero-tolerance policies that prohibit cannabis use entirely, including use outside of work, may be overly broad and are incompatible with the results of this study.”

Problems with the Cannabis-in-the-Workplace Study

Problems with the Cannabis-in-the-Workplace Study

While the results may be more-or-less favourable to cannabis consumers, the study’s methodology isn’t without criticism. Consider,

Sample recruitment

The study used a split-panel longitudinal design with individuals recruited mainly from pre-existing panels of households who agreed to participate. This could introduce selection bias. Using random digit dialling to recruit some respondents may also not ensure a representative sample.

Generalizability of Cannabis-in-the-Workplace Study

The study’s findings may be generalizable to only some Canadian workers, as the sample was limited to individuals at least 18 years old, currently employed, and working 15 or more hours per week for businesses employing five or more persons. This inclusion criterion might exclude specific subgroups of workers with different workplace injury risks or cannabis use patterns.

Self-reported data

The study relies on self-reported data for cannabis use, workplace injuries, and other variables. Self-reported data can be subject to recall bias, social desirability bias, and other measurement error sources, affecting the results’ accuracy.

Time lag in data collection

Researchers collected data on cannabis use and covariates a year before workplace injury assessment. This time lag may not capture immediate and more direct associations between cannabis use and workplace injuries.

Outcome measure

Researchers based outcome measures for workplace injury on a single yes/no item. This likely lacks the nuance needed to fully understand the nature and severity of injuries experienced by the participants.

Cannabis use assessment 

The study categorized participants based on past-year workplace and non-workplace cannabis use. Still, it does not provide information on the frequency, quantity, methods of cannabis consumption, or strain type. These could be essential to understanding the relationship between cannabis use and workplace injuries.

Imputation of missing data

Researchers used multiple imputations to address missing data. Still, the process might introduce additional uncertainty in the results, depending on the assumptions made during imputation.

Statistical approach 

While researchers used regression analysis to estimate associations, we cannot infer causality from observational studies.

Cannabis in the Workplace

This isn't the first study to examine cannabis in the workplace

This isn’t the first study to examine cannabis in the workplace. In 2021, the National Bureau of Economic Research found legal cannabis resulted in higher productivity and a decrease in workplace injuries.

But, like the above study, this was merely an association. Whether cannabis can cause workplace injuries (or prevent them) is still an open question.

But so far, based on available research, consuming cannabis during your off-hours isn’t negatively impacting your work performance the following day.