<p>While attention-deficit/hyperactivity disorder (ADHD) medication is effective for core symptoms, its broader and progressive impacts remain underexplored. This study evaluated real-world changes in ADHD symptoms and impairments, co-occurring psychiatric symptoms, physical measures, and health behaviors following ADHD medication initiation in adults. Data were drawn from a remote monitoring cohort recruited from adult ADHD clinic waiting lists in the United Kingdom and Spain. Participants completed 4-weekly smartphone-based self-reports and continuously wore a wearable device to monitor behaviors such as physical activity and sleep. We additionally developed novel wearable-derived features to approximate restlessness. A subset of 176 participants with valid baseline (off-medication) and up to three 4-weekly on-medication assessments was included. Compared to the off-medication phase, the on-medication phase was significantly associated with improvements in ADHD symptoms and impairments, as well as reductions in depression, anxiety, irritability, and aggression. Additional changes included reduced alcohol use, healthier diet, elevated heart rate, lower blood pressure, reduced waist circumference, increased physical activity, less restlessness, and improved sleep quality. Several domains showed significant progressive changes, including continued improvements in ADHD symptoms, impairments, and irritability; rising heart rate; declining body weight; and delayed sleep timing. These findings suggest ADHD medication in adults is associated with broad real-world benefits alongside some potential concerns, such as elevated heart rate and delayed sleep. This study highlights the potential of remote monitoring technologies to capture multidimensional treatment responses in daily life and provides a foundation for future research to support both clinical care and self-management in ADHD.</p>