An initial opioid prescription with a greater number of pills is associated with a greater risk for future long-term opioid use, yet few interventions have reliably influenced individual clinicians' prescribing. Our objective was to evaluate the effect of feedback interventions for clinicians in reducing opioid prescribing. The interventions included feedback on a clinician's outlier prescribing (individual audit feedback), peer comparison, and both interventions combined. We conducted a four-arm factorial pragmatic cluster randomized trial at forty-eight emergency department (ED) and urgent care (UC) sites in the western US, including 263 ED and 175 UC clinicians with 294,962 patient encounters. Relative to usual care, there was a significant decrease in pills per prescription both for peer comparison feedback (-0.8) and for the combination of peer comparison and individual audit feedback (-1.2). This decrease was sustained during follow-up. There were no significant changes for individual audit feedback alone, and no interventions changed the proportion of encounters with an opioid prescription.