he rising use and misuse of opioids is a national and international crisis that contributes significantly to opioid-related deaths, particularly in young adults. 1,2 In Canada, between January 2016 and June 2019, there were more than 13 900 apparent opioid-related deaths and 17 000 opioid-related hospital admissions. 3 In Canada and the United States, physicians prescribe higher quantities of opioids than in other countries 4,5 and the amount prescribed is often greater than is needed, as evidenced by the large numbers of unused opioids. 6,7 This may lead to longterm use in opioid-naive patients, 8,9 misuse by others in the household 10,11 and diversion (i.e., transfer of a medication from a lawful to unlawful distribution or use). 12 Surgeons commonly prescribe opioid analgesics to treat acute postoperative pain. In the US, despite writing only 1.8% of all medication prescriptions, surgeons accounted for 9.8% of all opioid prescriptions. 13 Breast cancer is the most common cancer in women in Canada, occurring in 1 in 8 females, with 27 000 new cases in 2019. 14 Breast surgery is commonly used to treat benign and malignant conditions. Postoperative pain management practices in breast surgery are variable among surgeons in the US, 15,16 with high rates of opioid analgesic overprescription, 5 despite recent literature that suggests 5 days is the appropriate length of time that opioids should be prescribed for breast surgery, if prescribed at all. 17 A recent Canadian study showed that patients undergoing breast surgery can achieve adequate pain control with minimal to no postoperative opioids. 18 To better evaluate prescribing practices, the Ontario Ministry of Health and Long-Term Care mandated data collection on Variation in opioid filling after same-day breast surgery in Ontario, Canada: a population-based cohort study