BACKGROUND: Cannabis was legalised for medical purposes in 2016. Uptake was initially slow, but since 2019 there has been a large increase in the number of Australians who have been prescribed cannabis for medical reasons. Yet a significant number of consumers continue to treat their medical conditions via illicitly-sourced cannabis. Little is known about how these two groups of medical cannabis consumers differ. METHODS: The anonymous Cannabis-As-Medicine Survey 2022-2023 (CAMS-22) was available for completion online from December 2022 to April 2023 to adult Australians who had used cannabis to treat a medical condition in the previous year. Recruitment occurred through social media, consumer forums, and medical practices. Questions included demographic characteristics, patterns of cannabis use, conditions treated, and self-rated effectiveness. RESULTS: Of the 3323 respondents included in these analyses, 2352 (73%) mainly used prescribed medical cannabis, 871 (27%) mainly used illicit. Prescribed users were significantly more likely than illicit users to have had their health condition diagnosed (OR = 1.7, 95% CI 1.3, 2.2), to consume their cannabis via oral (OR = 1.9; CI 1.5, 2.4) or vaporised (OR = 5.2; CI 4.0, 6.8) routes, and to be sure of the composition of their medical cannabis (OR = 25.0; CI 16.7, 50.0). Prescribed users were significantly less likely to have used cannabis non-medically before medical use (OR = 0.6, CI 0.5, 0.7), consume cannabis via smoked routes (OR = 0.2, CI 0.1, 0.2), and to report any side effects (OR = 0.1; CI 0.1, 0.2). The most common conditions among both prescribed and illicit users were pain (37%), mental health (36%), and sleep (15%) conditions. Prescribed users were significantly more likely to use cannabis to mainly treat a pain (OR = 1.3; CI 1.1, 1.5) or sleep condition (OR = 1.4; CI 1.1, 1.7) and less likely to treat a mental health condition (OR = 0.8; CI 0.7, 0.9). There were no between-group differences in effectiveness with 97% saying medical cannabis had improved their symptoms. CONCLUSIONS: From a harm-reduction perspective there is much to recommend prescribed medical cannabis; it has fewer side-effects than illicit, is used more safely (oral or vaporised versus smoked routes), gives consumers greater certainty regarding the composition and quality of their medicine, and does not risk exposure to the criminal justice system. Of concern, however, is the apparent willingness of prescribers to prescribe for indications for which there is limited evidence of efficacy, such as mental health and sleep conditions.