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The key distinction
Same drug class, different clinical purpose.
Both naloxone and naltrexone are opioid antagonists, meaning they block opioid receptors. But they are used in entirely different clinical contexts, at different doses, and for different durations. Confusing them is common, including among clinicians in non-addiction specialties.
Naloxone (Narcan)
A short-acting opioid antagonist used for emergency reversal of opioid overdose. Naloxone is administered in overdose emergencies, including by injection or intranasal spray. Its effects last 30–90 minutes, which may be shorter than the opioid it is reversing. It is also the antagonist component in Suboxone (buprenorphine/naloxone), where it serves as a deterrent against injection misuse.
Naltrexone (ReVia, Vivitrol)
A long-acting opioid antagonist used for relapse prevention in patients who have already detoxified from opioids. Oral naltrexone (ReVia) is taken daily; Vivitrol is a monthly extended-release injection. Naltrexone blocks opioid receptors, substantially reducing or preventing the effects of opioids during its active period.
Practical differences
When each is used.
Naloxone — emergency use
Naloxone is used in acute overdose situations. It is widely available in the United States, often without a patient-specific prescription, depending on state rules. and is widely distributed through harm reduction programs. It does not treat opioid use disorder — it reverses an acute overdose event. Patients who receive naloxone for overdose reversal should be connected with ongoing treatment.
Naltrexone — maintenance treatment
Naltrexone requires that a patient be fully detoxified from opioids before starting — otherwise it will precipitate acute withdrawal. This detoxification requirement is a significant barrier for many patients and is one reason naltrexone has lower treatment initiation rates than buprenorphine in real-world settings.
Naloxone in Suboxone
The naloxone in Suboxone is present at a low dose specifically to deter injection misuse. When Suboxone is taken as prescribed sublingually, naloxone is poorly absorbed and is not considered the primary therapeutic component.
Sources
Where this information comes from.
FDA: Medications for Opioid Use Disorder
Overview of naloxone and naltrexone — mechanisms, approvals, and clinical uses.
Federal overview of naltrexone for OUD including oral and extended-release injectable forms.
NIDA: Medications for Opioid Use Disorder
Plain-language comparison of buprenorphine, methadone, and naltrexone for OUD treatment.