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Emergency department visits during the 4/20 cannabis celebration
  1. John A Staples1,2,
  2. Ketki Merchant1,
  3. Shannon Erdelyi3,
  4. Adam Lund3,
  5. Jeffrey R Brubacher2,3
  1. 1 Department of Medicine, The University of British Columbia, Vancouver, British Columbia, Canada
  2. 2 Centre for Clinical Epidemiology & Evaluation (C2E2), Vancouver, British Columbia, Canada
  3. 3 Department of Emergency Medicine, The University of British Columbia, Vancouver, British Columbia, Canada
  1. Correspondence to Dr John A Staples, Department of Medicine, The University of British Columbia, Vancouver, BC V6Z 1Y6, Canada; jstaples1{at}


Background Annual ‘4/20’ cannabis festivals occur around the world on April 20 and often feature synchronised consumption of cannabis at 4:20 pm. The relationship between these events and demand for emergency medical services has not been systematically studied.

Methods We conducted a population-based retrospective cohort study in Vancouver, Canada, using 10 consecutive years of data (2009–2018) from six regional hospitals. The number of emergency department (ED) visits between 4:20 pm and 11:59 pm on April 20 were compared with the number of visits during identical time intervals on control days 1 week earlier and 1 week later (ie, April 13 and April 27) using negative binomial regression.

Results A total of 3468 ED visits occurred on April 20 and 6524 ED visits occurred on control days. A non-significant increase in all-cause ED visits was observed on April 20 (adjusted relative risk: 1.06; 95% CI 1.00 to 1.12). April 20 was associated with a significant increase in ED visits among prespecified subgroups including a 5-fold increase in visits for substance misuse and a 10-fold increase in visits for intoxication. The hospital closest to the festival site experienced a clinically and statistically significant 17% (95% CI 5.1% to 29.6%) relative increase in ED visits on April 20 compared with control days.

Interpretation Substance use at annual ‘4/20’ festivals may be associated with an increase in ED visits among key subgroups and at nearby hospitals. These findings may inform harm reduction initiatives and festival medical care service planning.

  • emergency care systems
  • emergency department
  • mass gathering medicine
  • drug abuse

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  • Contributors JAS was responsible for study concept, acquisition of the data and drafting of the manuscript. JAS, KM, SE, and JRB were responsible for study design and analytic strategy. SE and JAS had full access to all study data were responsible for the integrity of the data and the accuracy of the data analysis. All authors were responsible for critical revision of the manuscript.

  • Funding This work was supported by the Vancouver Coastal Health Research Institute (grant number not applicable). Funding organisations were not involved in the design and conduct of the study; collection, management, analysis and interpretation of the data; or preparation, review and approval of this manuscript.

  • Competing interests AL has worked as an event physician and/or medical director at hundreds of major planned events in Canada. He has a minority ownership interest in an event medical services company. All other authors report no competing interests.

  • Patient consent for publication Not required.

  • Ethics approval The University of British Columbia Clinical Research Ethics Board approved the study and waived the requirement for individual consent (UBC CREB number H18-02201).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement No data are available.