The MOR mediates opioids’ analgesiceffects and abuse liability. Buprenorphine,methadone, naloxone, and naltrexoneare among the pharmacotherapies used to treat opioid use disorders(OUD) (Figure )., Buprenorphine, a partial MOR agonist, and methadone, a full MORagonist, are used to treat OUD through opioid replacement or detoxificationtherapy. The gene discussed is OPRM1; the disease is opioid use disorder.