We propose a Hybrid Type 1 implementation- effectiveness trial of an adapted collaborative care model with peer-specialists as care managers, to enhance screening and treatment for mental health disorders/substance use disorders (MHD/SUD) with resultant improvement in rates of HIV viral suppression and care engagement in an HIV clinic setting. Collaborative care (CC), the use of a care manager/team to facilitate and coordinate integration of mental health and substance use services with primary care, is a well-established evidence-based model. We intend to adapt CC by training and supporting peer specialist to function as care managers. We will then rigorously evaluate peer-supported CC as a component of a multidisciplinary team including the HIV care provider and an addiction psychiatry consultant as an implementation strategy for MHD/SUD screening and treatment in a continuity HIV care practice. We will compare this peer-supported CC to usual care (UC) referral to psychiatric care or a SUD treatment program at the discretion of the primary care provider and evaluate the implementation process using the RE-AIM framework.