New US research has found that medicinal cannabis use declined in states where recreational programs became legal.
A team from the University of Michigan Medical School and the Centres for Disease Control and Prevention found that, although enrolment in medicinal cannabis programs grew overall between 2016 and 2022, it dropped in states that had legalised non-medical use.
The researchers carried out an ecological study with repeated measures of people holding medical cannabis licences and clinicians authorising those licences across the US between 2020 and 2022.
Their analysis covered 39 jurisdictions — 38 states and Washington D.C. — that permitted medical cannabis use.
Among those jurisdictions, 34 reported patient numbers, 19 provided patient-reported qualifying conditions, and 29 reported the number of authorising clinicians.
Across all jurisdictions, patient enrolment rose by 33 per cent between 2020 and 2022, climbing from 3.1 million to 4.1 million.
Within the 15 jurisdictions where adult-use laws were active, however, 13 recorded falling enrolment during the same period.
From 2020 to 2022, the share of patient-reported qualifying conditions with substantial or conclusive evidence of therapeutic value fell from 70.4 to 53.8 per cent. Chronic pain was the most commonly reported qualifying condition, followed by anxiety and post-traumatic stress disorder.
The study appears in the Annals of Internal Medicine.
When combined with figures from a previously published analysis, the total number of patients using cannabis for medical purposes has grown by more than 600 per cent since 2016.
Cannabis is currently legal for medical use in 38 US states and for non-medical adult use in 23 states.
The substance remains classified as schedule I under the Controlled Substances Act — a designation that has hampered research into its health effects and discouraged physicians from recommending it as a treatment — though the Department of Health and Human Services recently recommended it be rescheduled to schedule III.
