Why is methadone prescribed as a maintenance therapy for patients with opioid (morphine) use disorder?

Methadone is a long-acting full opioid agonist used in medication-assisted treatment (MAT) for opioid use disorder. Its long half-life (24-36 hours) produces stable plasma levels that prevent the peaks and troughs associated with short-acting opioids like heroin or morphine, thereby preventing withdrawal symptoms and reducing drug cravings. Methadone does NOT have no side effects — it causes dependence, constipation, QT prolongation, and respiratory depression. It does cause physical dependence (patients must be gradually tapered when discontinuing). Its therapeutic advantage is controlled dispensing through licensed clinics, stabilization of patients to allow social reintegration, and harm reduction by eliminating illicit drug use.