AI-powered mental health apps have attracted growing interest as a low-cost way to expand care. Yet questions remain about their effectiveness, safety, and whether they may crowd out psychotherapy. We evaluate one such app in a randomized controlled trial among 1,964 Mexican women with mild to severe psychological distress. Over six months, app access improved mental health by 0.3 standard deviations with no evidence of harm, improved sleep quality, increased healthful behaviors, and reduced mis...