RecruitingPhase 4Drug trialAssessment of Metformin for Restoration of Immune Homeostasis in HIV+ and HIV- Individuals With a History of Injection Drug UseThis randomized clinical trial (RCT) evaluates whether metformin can reduce systemic inflammation and improve immune function in individuals with a history of injection drug use, with or without HIV. Participants will receive metformin or placebo and undergo immune system assessments, including vaccine response evaluations.