Nalmefene is an opioid receptor antagonist primarily used in the treatment of alcohol dependence and for the reversal of opioid overdose. For alcohol dependence, it helps reduce the urge to drink and prevents relapse by blocking the effects of endogenous opioids in the brain, which contribute to the rewarding effects of alcohol. This facilitates reduced alcohol consumption as part of a comprehensive treatment plan that includes counseling and support. Additionally, nalmefene is used in emergency settings to antagonize the effects of opioids on the central nervous system, thereby reducing respiratory depression and other life-threatening symptoms in cases of opioid overdose. It requires close medical supervision.