Interrupted time series analysis of Canadian legal cannabis sales during the COVID-19 pandemic

Abstract

Introduction: There were repeated reports of increased cannabis sales, use and health impacts in Canada during the COVID-19 pandemic. However, it was unclear whether the increases were due to pandemic effects or industry expansion.

Methods: We performed interrupted time series regressions of monthly per capita legal cannabis sales from March 2019 to February 2021, first with national averages, then with provincial/territorial data after adjusting for store density. We considered two interruption alternatives: January 2020, when product variety increased; and March 2020, when pandemic restrictions began.

Results: The provincial/territorial regression with the January interruption explained R² = 69.6% of within-jurisdiction variation: baseline monthly per capita sales growth averaged $0.21 (95% confidence interval [CI] 0.15, 0.26), sales immediately dropped in January by $1.02 (95% CI -1.67, -0.37), and monthly growth thereafter increased by $0.16 (95% CI 0.06, 0.25). With the March interruption, the regression instead explained 68.7% of variation: baseline sales growth averaged $0.14 (95% CI 0.06, 0.22), there was no immediate drop and growth thereafter increased by $0.22 per month (95% CI 0.08, 0.35).

Discussion and conclusions: Increasing cannabis sales during the pandemic was consistent with pre-existing trends and increasing store numbers. The extra increased growth was more aligned with January's new product arrivals than with March's pandemic measures, though the latter cannot be ruled out. We found little evidence of pandemic impacts on Canada's aggregate legal cannabis sales. We therefore caution against attributing increased population-level cannabis use or health impacts primarily to the pandemic.

Keywords: COVID-19 pandemic; cannabis; health economics; interrupted time series analysis; legalisation.

Figure 1

National monthly legal cannabis retail sales, from March 2019 to February 2021, in Canadian dollars per resident age 15+. Dots represent observed monthly sales, solid lines represent regression‐predicted sales assuming a March 2020 interruption and vertical bars represent total licensed cannabis stores. The vertical dashed line separates the pre‐pandemic and pandemic periods.