Extended-release opioids are often prescribed to manage postoperative pain despite being difficult to titrate to analgesic requirements and their association with long-term opioid use. An Australian/New Zealand organisational position statement released in March 2018 recommended avoiding extended-release opioid prescribing for acute pain. This study aimed to evaluate the impact of this organisational position statement on extended-release opioid prescribing among surgical inpatients. Secondary objectives included predictors and clinical outcomes of prescribing extended-release opioids among surgical inpatients. We conducted a retrospective, dual centre, 11-month before-and-after study and time-series analysis by utilising electronic medical records from two teaching hospitals in Sydney, Australia. The primary outcome was the proportion of patients prescribed an extended-release opioid. For surgical patients prescribed any opioid (n = 16,284), extended-release opioid prescribing decreased after the release of the position statement (38.4% before vs. 26.6% after, p < 0.001), primarily driven by a reduction in extended-release oxycodone (31.1% before vs. 14.1% after, p < 0.001). There was a 23% immediate decline in extended-release opioid prescribing after the position statement release (p < 0.001), followed by an additional 0.2% decline per month in the following months. Multivariable regression showed that the release of the position statement was associated with a decrease in extended-release opioid prescribing (OR 0.54, 95%CI 0.50–0.58). Extended-release opioid prescribing was also associated with increased incidence of opioid-related adverse events (OR 1.52, 95%CI 1.35–1.71); length of stay (RR 1.44, 95%CI 1.39–1.51); and 28-day re-admission (OR 1.26, 95%CI 1.12–1.41). Overall, a reduction in extended-release opioid prescribing was observed in surgical inpatients following position statement release.