PROJECT SUMMARY / ABSTRACT The opioid crisis is an epidemic with devastating health, social, and economic consequences for the United States. From 1999–2018, almost 450,000 people died from an overdose involving any opioid, including prescription and illicit opioids. Three million US citizens and 16 million individuals worldwide have had or currently suffer from opioid use disorder (OUD). The total economic burden of the opioid crisis in the US is estimated to be more than $200 billion annually. Treatment for OUD involves medication assisted treatment (MAT) combined with counseling or behavioral therapy to manage the illness, achieve and sustain better health, and improve quality of life. Rates of recurrent drug use are high, and access to counseling is limited and costly. While MAT is standard of care and highly effective at reducing acute morbidity and mortality, there are advantages to treatment approaches tailored to address an individual patient’s drug use patterns and drug-related medical, psychiatric, and social problems. While mobile tools exist to support OUD treatment, these products offer only generalized information and not personalized feedback that is responsive to each person’s current status to support their individual recovery. In Phase I, we developed KIOS, an innovative software platform using nonlinear control theory. KIOS tracks multiple interacting symptoms (e.g., craving, mood, pain) to map patient trajectories and deliver timely evidence-based intervention strategies, responding directly to patient-reported needs. Accessible via mobile devices, KIOS provides patients on demand individualized advice and reinforcement of lifestyle interventions to improve self-management during MAT. Phase I beta testing demonstrated significant reductions in key symptoms of OUD and high levels of engagement, usability and patient satisfaction. This project completes development of KIOS as a prescription digital health therapeutic suitable for FDA approval concomitant to MAT to treat OUD. This innovative tool to help patients manage OUD has the potential to have a profound impact on public health and achieve significant commercial success. This Phase II STTR study has three Specific Aims which are designed to attain FDA medical device approval: Specific Aim 1: Enhance Software Design and Features Specific Aim 2: Comply with Regulatory Requirements Specific Aim 3: Evaluate KIOS in a 12-week Randomized Controlled Trial