Opioid Prescribing in Canada following the Legalization of Cannabis: A Clinical and Economic Time-Series Analysis.

On 17 October 2018 recreational cannabis became legal in Canada, thereby increasing access and reducing the stigma associated with its use for pain management. This study assessed total opioid prescribing volumes and expenditures prior to and following cannabis legalization. National monthly claims data for public and private payers were obtained from January 2016 to June 2019. The drugs evaluated consisted of morphine, codeine, fentanyl, hydrocodone, hydromorphone, meperidine, oxycodone, tramadol, and the non-opioids gabapentin and pregabalin. All opioid volumes were converted to a mean morphine equivalent dose (MED)/claim, which is analogous to a prescription from a physician. Gabapentin and pregabalin claims data were analyzed separately from the opioids. Time-series regression modelling was undertaken with dependent variables being mean MED/claim and total monthly spending. The slopes of the time-series curves were then compared pre- versus post-cannabis legalization. Over the 42-month period, the mean MED/claim declined within public plans (p < 0.001). However, the decline in MED/claim was 5.4 times greater in the period following legalization (22.3 mg/claim post vs. 4.1 mg/claim pre). Total monthly opioid spending was also reduced to a greater extent post legalization ($Can267,000 vs. $Can95,000 per month). The findings were similar for private drug plans; however, the absolute drop in opioid use was more pronounced (76.9 vs. 30.8 mg/claim). Over the 42-month period, gabapentin and pregabalin usage also declined. Our findings support the hypothesis that easier access to cannabis for pain may reduce opioid use for both public and private drug plans.