Objectives: We characterized trends in medical cannabis use; examined characteristics associated with medical cannabis use without medical authorization; and examined the association between recreational cannabis legalization and medical cannabis use in Ontario, Canada. Methods: Data were from a repeated, population-based, cross-sectional survey of adults (N = 19,543; 2014–2019). Cannabis use was categorized as either medical cannabis use, recreational cannabis use or no cannabis use. The analytical strategy included jointpoint regression, logistic regression and multinomial logistic regression. Results: Medical cannabis use increased from 4 % to 11 % (Annual Percentage Change [APC]: 25 %, 95 % Confidence Interval [CI]: 17 %–33 %) and recreational cannabis use increased from 9 % to 15 % (APC: 9 %, 95 % CI: 3 %-15 %) between 2014 and 2019. Being 18 to 29 years old compared with being 65+ years old was associated with an increased likelihood of medical cannabis use without medical authorization (Odds Ratio [OR]: 4.05, 95 % CI: 2.12–7.72), while being of fair or poor self-perceived health compared with excellent, very good or good self-perceived health (OR: 0.61, 95 % CI: 0.40–0.95) was associated with a decreased likelihood of medical cannabis use without medical authorization. Recreational cannabis legalization was associated with an increased likelihood of medical cannabis use compared with no cannabis use (OR: 1.48, 95 % CI: 1.19–1.85) and of recreational cannabis use compared with no cannabis use (OR: 1.35, 95 % CI: 1.11–1.65). Conclusions: Although medical cannabis use increased, it was largely used without medical authorization. Guidance and education that encourages medical usage under clinical supervision is recommended, and mitigation of known barriers to medical cannabis authorization.