Which statement about initiating naltrexone for opioid use disorder is true?

• A. Is given as a mu agonist.
• B. Can be started without any withdrawal or detox.
• C. Is started only after complete abstinence for 6 months.
• D. Requires detoxification before initiation.

Answer: (D)

Initiating naltrexone for opioid use disorder hinges on detoxification because naltrexone is an opioid receptor antagonist. By blocking mu receptors, it prevents opioids from producing their effects. If opioids are still present in the body, starting naltrexone will abruptly displace them and trigger withdrawal symptoms, which can be dangerous and strongly discourage treatment adherence.

Therefore, treatment is started only after the patient has completed a detoxification period and is opioid-free for a suitable washout (the exact time depends on the specific opioid used, with longer periods for methadone or long‑acting formulations). Once there is no remaining opioid in the system and withdrawal symptoms have resolved or are mild, naltrexone can be started to maintain abstinence by blocking the effects of any future opioid use.

Naltrexone is not a mu agonist, so it does not produce the opioid effects it aims to prevent. It does not require six months of abstinence before starting, and starting without any withdrawal or detox is unsafe because of the risk of precipitated withdrawal.