Despite concerns and recommendations, modified-release opioids are still commonly used for the management of acute pain following total hip and knee arthroplasty. There is a need to compare modified-release and immediate-release opioid use following these procedures, and to determine whether the use of modified-release opioids is safe or harmful. The primary objective of this study was to examine the impact of modified-release opioid use on the incidence of opioid-related adverse drug events compared with immediate-release opioid use among adult hospital inpatients following primary total hip or knee arthroplasty. In this multicentre propensity score matched cohort study, modified-release opioid use in the acute postoperative period is associated with an increased risk of experiencing opioid-related adverse events after total hip or knee arthroplasty compared with those given immediate-release opioids only. Further, patients given modified-release opioids experienced a higher incidence of constipation and in-hospital falls, as well as a longer length of hospital stay compared with patients given immediate-release opioids only. Join our Editor Dr Helen Laycock as she discusses the study and its implications with the authors.