Opioid use disorder is a medical term used to describe the chronic misuse of opioids, a class of drug commonly prescribed to treat prolonged or severe pain by blocking pain signals between the brain and the body. Patients with this disorder experience opioid addiction, severe withdrawal symptoms and increased tolerance over time. OUD affects people of all social, economic and educational backgrounds. According to the U.S. Department of Health and Human Services, 1.6 million Americans had an OUD in 2019.