Opioids for back and neck pain: the OPAL trial – Authors' reply

There are different opioid classes with different pharmacological profiles.4 However, within the morphine-like (4,5-epoxymorphinans) class, each opioid provides an equivalent analgesic effect based on morphine equivalent dose.4 Our systematic review in chronic low back pain found no difference in analgesic effects when comparing trials that investigated different opioids.5 We agree that the OPAL results might not be generalisable to all patients with acute low back and neck pain, including those experiencing hyperacute pain requiring immediate pain relief in the emergency department. The treatment estimates were precise, and we showed between-group differences for several outcomes—but those differences favoured placebo. The OPAL trial was funded by Australia's National Health and Medical Research Council, University of Sydney Faculty of Medicine and Health, and ReturnToWorkSA.