Background: One in four Veterans presenting to VA primary care screen positive for hazardous drinking. However, due to barriers such as Veterans’ stigma about seeking alcohol use treatment and challenges with traveling to VA, most of these Veterans do not receive any alcohol-related care. Mobile applications (apps) are an innovative means of expanding access to alcohol use treatment. The evidence for mobile apps, such as “Step Away”, to improve drinking outcomes is emerging. Nevertheless, poor patient engagement remains the Achilles’ heel of these apps. Peer Specialists (“Peers”) can facilitate Veterans’ engagement with mobile apps intended for self-management of hazardous drinking by helping to orient patients to these apps and by providing technical support and accountability. In a VA HSR&D pilot study (PPO 16-305), we created a Veteran version of the Step Away app (“Stand Down: Think Before You Drink”) and conducted an open trial in which Veterans with hazardous drinking used the app while receiving Peer phone support. The intervention (“Peer- Supported [PS]-Stand Down”) was highly acceptable to patients, and patients reported significant improvements in drinking outcomes. These data provide a strong foundation for a larger pragmatic trial to test the effectiveness of the Stand Down app and PS-Stand Down to reduce hazardous drinking among Veterans seen in primary care, relative to the current standard of care that these patients receive. Significance: By capitalizing on a high-value workforce shown to improve Veterans engagement in care (i.e., Peers), this research can expand access to alcohol care for Veterans with low staff burden and, in turn, reduce the long-term health consequences associated with untreated hazardous drinking. Our proposed research responds to HSR&D priorities of Access to Care, Mental Health, and Virtual Care, and the VA MISSION Act. Innovation and Impact: Poor patient engagement severely limits the potential effectiveness of mobile apps for self-management of alcohol use problems. Use of Peers to enhance patients’ engagement with such apps is a novel approach to overcoming this problem. Peers are ideally suited to this role by virtue of their lived experience with addiction. This approach represents a novel application of the supportive accountability model of adherence to e-health interventions. Combined with VA’s expansion of Peers on Patient Aligned Care Teams (PACT), PS-Stand Down, if shown to be effective, can transform the delivery of care for Veterans in primary care who screen positive for hazardous drinking. Specific Aims: We propose to evaluate whether the Stand Down app reduces drinking among Veteran primary care patients who engage in hazardous drinking, and for whom PS-Stand Down is more effective than the app alone. Aim 1: Test whether Stand Down (vs. Usual Care; UC) and PS-Stand Down (vs. UC and vs. app only) predicts better drinking outcomes, and test mediators of these effects. Aim 2: Test for differenc...