The Substance Use and Comorbidity Lab is based within the Division of Geriatrics, Gerontology, and Palliative Care in the Department of Medicine at the University of California San Diego. We aim to address the growing prevalence of substance use (alcohol, cannabis, sedatives, hypnotics, non-legal drugs) among older adults and adults living with multiple chronic diseases. The lab employs a public health and harm reduction lens to reduce the harms related to psychoactive substance use among a diverse population of older adults. This includes improving the health of older adults living with substance use disorder and to increase the delivery of evidence-based substance use disorder treatment and harm reduction interventions. Our research group conducts a range of research studies, including epidemiological, qualitative, health services, and the development and testing of interventions that focus on the intersection of substance use, chronic disease, and aging, especially among populations made vulnerable.