PROJECT SUMMARY Type 1 diabetes (T1D) is a significant public health problem, with some three million Americans living with the illness. Although extensive research has examined factors that facilitate or impede T1D management during childhood and adolescence, much less is known about the high-risk time of emerging adulthood. Less than one-third of emerging adults engage in self-management consistent with recommendations for blood glucose checking and diet, and only 17% meet recommendations for blood glucose control, placing emerging adults at risk for serious long-term complications. We theorize these risks occur because emerging adults are still developing the self-regulation skills to manage T1D independently and lack the necessary social resources to manage their illness as parental involvement declines and new relationships at work and in college occur. There is a critical need to intervene, however, few high-quality interventions exist to address the unique needs of emerging adults with T1D. The scientific premise is that an intervention targeting self-regulation (setting goals, planning) and social-regulation (disclosing to others so they can provide social support) will be beneficial for meeting the challenges of managing T1D during emerging adulthood. The research is innovative in testing the efficacy of a theory-based intervention to target self-regulation and leverage social relationships in the daily lives of a sample of ethnically/racially diverse emerging adults. FAMS-T1D is a newly adapted intervention based on a highly effective intervention (FAMS-Family/friend Activation to Motivate Self-Care) developed for adults with type 2 diabetes (T2D) that involves three components: 1) phone-based coaching to improve patients’ skills in goal pursuit and managing social relationships, 2) text messaging to patients to facilitate self- regulation and social-regulation, and 3) text messaging to a support person (SP) to improve dialogue with and support for the patient. The study compares the intervention to control (enhanced treatment as usual). Extensive preliminary data of the investigative team support the need for the intervention in emerging adults with T1D and the efficacy of the intervention for adults with T2D. In Aim 1, we evaluate the effects of the 6- month intervention on A1c, self-management, and diabetes distress at 6-, 9-, and 12-months post baseline with a diverse sample of 280 emerging adults and SPs recruited across two sites. In Aim 2, we examine whether the effects on outcomes occur through improvements in patients’ reports of self-regulation (planning, self- efficacy, self-regulation failures) and social-regulation (disclosure to others; helpful and harmful involvement of family and friends). In Aim 3, we evaluate how the intervention improves SP reports of their involvement without increasing SP burden. In Aim 4, we explore the time course of intervention effects on time in range using continuous glucose monitoring data fr...