What is the primary action of naltrexone?

Naltrexone primarily functions as an opioid receptor antagonist, meaning it blocks the effects of opioids at their receptors in the brain. This action makes naltrexone effective in the treatment of opioid dependence and in reducing cravings for alcohol, as it inhibits the pleasurable effects that opioids and alcohol produce. By preventing opioids from binding to their receptors, naltrexone helps to support patients in recovery by reducing the rewarding effects typically associated with opioid use, thus decreasing the likelihood of relapse.

Other options involve mechanisms or indications that are unrelated to the primary action of naltrexone. Enhancing opioid effects would directly counteract its function as an antagonist, managing asthma pertains to a completely distinct line of medications, and relieving anxiety is not related to naltrexone's primary role in blocking opioid receptors.