Which medication is a full opioid agonist used in maintenance therapy?

• A. Methadone
• B. Buprenorphine
• C. Naltrexone
• D. Naloxone

Answer: (A)

In maintenance therapy for opioid use disorder, a full opioid agonist is used because it fully activates mu-opioid receptors to suppress withdrawal and cravings over the long term. Methadone fits this role as a long-acting, full mu-opioid receptor agonist. It provides steady receptor activation, stabilizes mood and function, reduces illicit use, and lowers the risk of withdrawal symptoms when used as prescribed.

Buprenorphine, by contrast, is a partial agonist at the mu receptor. It activates the receptor but to a limited extent, giving a ceiling effect that lowers overdose risk but does not produce the same full receptor activation as methadone, so it’s not a full agonist.

Naltrexone and naloxone are opioid antagonists. They bind the receptors without activating them and block or reverse opioid effects. Naloxone is used for overdose reversal, and naltrexone is used to prevent relapse after detox, not for ongoing maintenance with agonist effects.