Key PointsQuestionIs mifepristone effective for adenomyosis treatment?FindingsIn this randomized clinical trial of 134 participants with adenomyosis pain symptoms, the participants in the mifepristone group and had significantly greater improvement in pain scores than the placebo group. All the secondary outcomes, including hemoglobin, platelet count, and uterine volume, showed significant improvements in the mifepristone group, and there were no serious adverse events.MeaningThis randomized clinical trial found that mifepristone was effective and safe for the treatment of adenomyosis, which supports the repositioning of this drug as a new treatment option for adenomyosis.