Els C, Jackson TD, Tsuyuki FT, Aidoo H, Wyatt G, Sowah D, Chao D, Haoffman H, Kunyk D, Milen M, Stewart-Patterson C, Dick BD, Farnan P, Straube S. Impact of cannabis use on road traffic collisions and safety at work: systematic review and meta-analysis. Canadian Journal of Addition 2019;10(1):8-15. (abstract and link to article on Ovid)

Why was this study conducted?

The legalization of recreational cannabis has raised safety concerns about its effects on workplace and traffic safety.

What does this study add?

The authors conducted a systematic review and meta-analysis of studies to date looking at the safety implications of cannabis use. Of 864 publications retrieved, 11 unique case-control studies investigating traffic collisions were identified from seven countries. Most involved general population drivers in normal traffic, although one was conducted among professional drivers. The meta-analysis was conducted on a total of 7,443 cases. Compared to those who did not, individuals who were positive for tetrahydrocannabinol (THC) or its metabolites had twice the risk of road traffic collision (Odds Ratio = 2.49, 95% confidence interval 1.68-3.71).

Is there anything else I should know?

No studies investigating the effect of THC on workplace safety could be located. Nevertheless, the authors extrapolate from the meta-analysis of traffic studies that those who work in hazardous environments or perform safety-sensitive tasks should refrain from cannabis for at least 24 hours prior to entering the work setting.

Author Details

The latest scientific evidence on this topic was reviewed by the Centre's leadership team. This research summary is written by Corinne Hodgson, DHealth, assessed for accuracy by Dr. James MacKillop, PhD. There are no conflicts of interest. Questions regarding this piece should be directed to Dr. James MacKillop (jmackill@mcmaster.ca).