Opioid use disorder (OUD) is a treatable medical illness with three medications FDA approved for treatment. However, persons with OUD report significant sleep disturbance, even when treated with medications for opioid use disorder, leading to high rates of relapse. In this project, we will investigate a special set of photosensitive neurons in the retina as an underlying mechanism for circadian rhythm and sleep disturbance from opioid use and medications for OUD that could lead to novel intervention and improve treatment outcomes.