Abstract Introduction Although cannabis is frequently used worldwide, its impact on respiratory health is characterised by controversy. Objective To evaluate the association between cannabis use and respiratory-related emergency room (ER) visits and hospitalisations. Methods A retrospective, population-based, cohort study was carried out, linking health survey and health administrative data for residents of Ontario, Canada, aged 12–65 years, between January 2009 and December 2015. Individuals self-reporting cannabis use within the past year were matched to control individuals (people who reported never using cannabis, or used cannabis only once, and more than 12 months ago) in upwards of a 1:3 ratio on 31 different variables, using propensity score matching...