Naloxone vs. Naltrexone vs. Narcan: What Is the Difference?

Key Takeaways

• Narcan is a brand name for naloxone — they are the same medication
• Naloxone is a short-acting opioid antagonist used to reverse overdoses in emergency situations
• Naltrexone is a long-acting opioid antagonist used to prevent relapse during addiction treatment
• The two medications serve completely different clinical purposes despite having similar-sounding names
• Naloxone is available over the counter; naltrexone requires a prescription and medical supervision

Opioid Antagonist: A medication that binds to opioid receptors in the brain without activating them, blocking the effects of opioid drugs. Both naloxone and naltrexone are opioid antagonists, but they differ significantly in duration of action, clinical use, and how they are administered.

The names naloxone, naltrexone, and Narcan create frequent confusion among patients, families, and even some healthcare workers. These medications share a pharmacological class — both are opioid antagonists — but they serve entirely different purposes in addiction medicine. Naloxone (brand name Narcan) is an emergency medication that reverses opioid overdoses within minutes. Naltrexone is a maintenance medication prescribed to reduce cravings and prevent relapse in people recovering from opioid or alcohol use disorders. Understanding the distinction is important for anyone navigating the treatment system.

Naloxone and Narcan: Same Drug, Different Names

Brand Name vs. Generic

Naloxone Hydrochloride: The generic name for the active pharmaceutical ingredient in Narcan. It is classified as a competitive opioid antagonist with rapid onset and short duration of action.

Narcan is simply the most well-known brand name for naloxone. The relationship is identical to that between Tylenol and acetaminophen — one is a brand name, the other is the generic drug name. Other brand names for naloxone products have included EVZIO (a discontinued auto-injector) and RiVive (a generic OTC nasal spray).

When people refer to “Narcan,” they are referring to naloxone. The terms are interchangeable in common usage, though healthcare professionals and pharmacists typically use the generic name naloxone.

How Naloxone Is Classified

The FDA classifies naloxone as an opioid antagonist. It is not a controlled substance, has no potential for abuse, and produces no psychoactive effects in people without opioids in their system. Naloxone is on the World Health Organization’s List of Essential Medicines and has been available in the United States since 1971.

Naloxone works by competitive binding at mu-opioid receptors. It has a higher affinity for these receptors than most opioid drugs, allowing it to displace opioids that are already bound. Its effects are temporary, lasting approximately 30 to 90 minutes depending on the route of administration.

Naltrexone: A Different Medication Entirely

How Naltrexone Works

Naltrexone: A long-acting opioid antagonist that blocks opioid receptors for 24 hours (oral form) or approximately 30 days (extended-release injection). Unlike naloxone, naltrexone is used as a maintenance medication for relapse prevention, not for emergency overdose reversal.

Naltrexone also binds to opioid receptors and blocks opioid effects, but it does so for a much longer period. Oral naltrexone (brand name ReVia) blocks receptors for approximately 24 hours per dose. Extended-release injectable naltrexone (brand name Vivitrol) provides blockade for approximately 30 days from a single injection.

The key pharmacological difference is duration. Naloxone acts within minutes and wears off in less than two hours. Naltrexone builds up in the system and maintains consistent receptor blockade over days or weeks.

Naltrexone for Addiction Treatment

The FDA has approved naltrexone for two indications:

• Opioid use disorder — naltrexone blocks the euphoric and sedating effects of opioids, reducing the motivation to use
• Alcohol use disorder — naltrexone reduces alcohol cravings and the rewarding effects of drinking, though the mechanism in alcohol use disorder involves the endogenous opioid system rather than exogenous opioids

Naltrexone is one of three FDA-approved medications for opioid use disorder, alongside buprenorphine (Suboxone) and methadone. It is also one of three FDA-approved medications for alcohol use disorder, alongside acamprosate (Campral) and disulfiram (Antabuse).

A critical requirement: naltrexone cannot be started until a person is fully detoxed from opioids, typically seven to fourteen days after the last opioid use. Starting naltrexone while opioids are still in the system triggers precipitated withdrawal — a sudden, severe withdrawal syndrome.

Key Differences Between the Two

Duration of Action

Feature	Naloxone	Naltrexone
Onset of action	2-5 minutes	1-2 hours (oral)
Duration	30-90 minutes	24 hours (oral) / 30 days (injectable)
Clinical context	Emergency	Maintenance treatment
Available OTC	Yes (nasal spray)	No — prescription required

Medical Uses and Indications

Naloxone has one primary medical use: reversing opioid overdoses. It is carried by first responders, stocked in emergency departments, and distributed to communities through harm reduction programs. It can also be found as a component in Suboxone (buprenorphine/naloxone), where it is included to deter injection misuse of the medication.

Naltrexone is prescribed as part of a comprehensive treatment plan for opioid or alcohol use disorders. It is not an emergency medication. Prescribers include addiction medicine physicians, psychiatrists, and primary care doctors who have evaluated the patient and confirmed they are appropriate candidates for antagonist therapy.

How They Are Administered

Naloxone is administered by:

• Nasal spray (Narcan, RiVive) — the most common community form
• Intramuscular injection — used by some first responders and harm reduction programs
• Intravenous injection — used in hospital emergency departments

Naltrexone is administered by:

• Daily oral tablet (ReVia, generic naltrexone) — 50 mg taken once daily
• Monthly intramuscular injection (Vivitrol) — 380 mg injected by a healthcare provider every four weeks

When Each Medication Is Used

Emergency Overdose Situations

Naloxone is the appropriate medication when someone is experiencing signs of opioid overdose: slow or stopped breathing, pinpoint pupils, blue lips or fingertips, unresponsiveness. According to NIDA, naloxone should be administered immediately in a suspected opioid overdose, followed by a call to 911. It is a rescue medication designed to keep a person alive until emergency medical services arrive.

Naltrexone has no role in overdose reversal. Its slow onset and oral or monthly injection administration make it entirely unsuitable for emergency use.

Ongoing Addiction Treatment

Naltrexone is the appropriate medication when a person has completed detoxification and is working to maintain abstinence from opioids or alcohol. It is typically prescribed as part of a treatment plan that includes counseling, behavioral therapy, and recovery support services.

Medication-Assisted Treatment (MAT): An evidence-based approach that combines FDA-approved medications (including naltrexone, buprenorphine, or methadone) with counseling and behavioral therapies to treat substance use disorders. SAMHSA considers MAT the standard of care for opioid use disorder.

Naloxone does not have a role in ongoing treatment beyond its inclusion as a deterrent component in Suboxone formulations. It is not prescribed for relapse prevention or craving reduction.

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This glossary entry is part of our Addiction Treatment Glossary. For more on naloxone specifically, see What Is Narcan (Naloxone)?. For a detailed comparison of naltrexone-based treatment with other MAT medications, read Vivitrol vs. Suboxone vs. Sublocade. To learn more about medication-assisted treatment options, visit our guide on MAT for opioid addiction.