Which medication is used as an opioid receptor antagonist for relapse prevention in opioid dependence?

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

Answer: (D)

Blocking opioid effects at the receptor level to prevent relapse is the idea here. Naltrexone is an opioid receptor antagonist that binds strongly to mu receptors and blocks opioids from producing their usual euphoric and rewarding effects. When started after detoxification, it prevents the reinforcing high from opioids, helping to sustain abstinence because any opioid taken won't produce the expected relief or pleasure. It’s important to begin after the patient is opioid-free to avoid precipitated withdrawal, and it can be given daily by mouth or as an extended‑release injection to aid adherence. By contrast, methadone and buprenorphine activate opioid receptors (they are an agonist and a partial agonist, respectively), so they are used for maintenance and craving/withdrawal reduction rather than as antagonists for relapse prevention. Naloxone is also an antagonist but is used mainly for acute overdose reversal due to its short action, not for preventing relapse.