How does naltrexone help in treating alcohol use disorder, and what are common formulations?

• A. Dopamine reuptake inhibitor; available as intramuscular injection only.
• B. Blocks mu-opioid receptors; available as daily oral and extended-release injectable.
• C. Serotonin receptor antagonist; available as a transdermal patch.
• D. Full agonist at mu receptor; available as IV infusion.

Answer: (B)

Naltrexone helps alcohol use disorder by blocking mu-opioid receptors in the brain. This reduces the rewarding effects of alcohol and lowers cravings, which helps prevent relapse and support abstinence or reduced drinking. It is not a dopamine reuptake inhibitor, not a serotonin receptor antagonist, and not a mu receptor full agonist, so those mechanisms described in other meds don’t apply to naltrexone. A practical point is that people must be opioid-free before starting to avoid withdrawal or precipitated withdrawal. In terms of formats, naltrexone is available as a daily oral tablet and as an extended-release injectable given monthly, with the oral form typically taken at 50 mg each day and the injectable providing month-long receptor blockade.