Abstract Objectives This study aimed to explore the incidence of adverse events (AEs) reported by patients when initiating medicinal cannabis treatment for chronic pain, and the association of cannabis constituents, dose and concomitant medicines with AE incidence. Methods Patient demographics, cannabis products and AE data were collected as part of the Cannabis Access Clinics Observational Study, and concomitant medicines were obtained from patient health summaries provided by referring doctors. Cannabis products were grouped by their constituents as either cannabidiol-only or containing both cannabidiol and Δ-9-tetrahydrocannabinol. Key findings From a total of 275 patients, each had a median of six concomitant medicines, with opioids (n =...