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What is the difference between naloxone and naltrexone?
Naloxone is a short-acting medication used to reverse opioid overdose. Naltrexone is a long-acting medication used to prevent return to use after detox. They have similar names but completely different uses.
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 to help prevent return to use 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 — ongoing 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.
Related
← All Learn topics · Vivitrol · What is Suboxone · Methadone vs Suboxone
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Common questions
Frequently asked
Can naloxone be used to reverse a Suboxone overdose?
Buprenorphine overdose is rare due to its ceiling effect, but high-dose naloxone can partially reverse buprenorphine. It requires higher doses than for full agonist opioids.
How quickly does naloxone work?
Naloxone nasal spray typically begins working within 2–5 minutes. Its effects last 30–90 minutes — shorter than most opioids — which is why repeat dosing and emergency services are needed.
Why does naltrexone require full detox first?
Naltrexone blocks opioid receptors completely. If taken while opioids are still active, it causes precipitated withdrawal. A period of complete opioid abstinence — sometimes called medically supervised withdrawal or simply cessation — is required before starting.
