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How Long Does Naltrexone Last in the Body?

Peter Manza, PhD profile image
Reviewed By Peter Manza, PhD • Updated Oct 24, 2023 • 4 cited sources

Oral naltrexone lasts between 24 and 72 hours. Naltrexone injections (Vivitrol) last for about a month. [1],[2]

You’ll feel the effects of either type of dose within an hour or two. The pill is eliminated from your body in hours, but the injection lasts longer.

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How Long Does it Take for Naltrexone to Work?

Quick Answer

Naltrexone begins to work the day that you take it, whether you take the oral or injectable version. You will begin to feel it working within an hour or two—this will likely include relief from opioid or alcohol cravings.

How Long Does Naltrexone Stay in Your System?

Naltrexone stays in your body within 24 hours and 30 days, depending on the administration method. 

Naltrexone is a prescription medication sold as Vivitrol (an injection) or ReVia (a pill). Naltrexone works by blocking opioid receptors, making a return to alcohol or opioids less intoxicating. If you slip and drink or use drugs, they won’t work in the same way they used to. You may be less tempted to slip again.[1]

Naltrexone is used as part of Medication for Addiction Treatment (MAT) programs and alcohol use disorder (AUD) programs. The U.S. Food and Drug Administration approved naltrexone in 1984.[1]

How Long Naltrexone Lasts by Administration Method

Pills Injection 
Daily Monthly 

Understanding How the Body Metabolizes Naltrexone 

Naltrexone is processed by the liver. The portions of the drug your body can’t use are processed by your liver and excreted. 

A drug’s half-life is important when considering how long a substance lasts in your body. This measurement tells you how long your body needs to remove half a dose of a drug. After about four half-lives, most drugs no longer work.[4] 

Naltrexone’s half-life depends on the administration method:

  • Injection: The drug’s half-life is five to 10 days.[2]
  • Oral ingestion: The drug’s half-life is four hours.[3]

Factors Affecting How Long Naltrexone Stays in Your System 

How quickly you’ll process naltrexone depends on multiple factors, including some that remain far outside your control.

Those factors include the following:

  • Age: Older people tend to process medications slower than younger people. 
  • Organ health: Naltrexone is metabolized by the liver. Underlying organ disease could make it harder for your body to process the medication. 
  • Genetics: Some people have genetic issues that interfere with how well they can process medications like naltrexone. 

How Long Is Naltrexone Detectable in the Body?

Naltrexone is not an intoxicating drug, and it’s not misused for recreational purposes. It won’t change how you feel or your ability to work or drive. 

How Long Naltrexone Is Detectable by Test Type

Sample TypeDetection Duration
Urine4 hours to months 
Blood 24 hours to months 
Saliva 24 hours to months
Hair90 days 

That said, naltrexone isn’t included in the standard drug tests, so it isn’t likely your employer or parole officer will test for it. Plus, you are legally allowed to take naltrexone for alcohol use disorder or opioid use disorder and cannot be discriminated against or punished for it.

Frequently Asked Questions About Naltrexone Duration

We’ve compiled some of the most commonly asked questions about the duration naltrexone stays in your system.

Does naltrexone work on the first day?

Yes. Naltrexone starts working on the first day, whether you’re using oral or injectable forms. It usually starts working within an hour or two.

How long does naltrexone last in your body to prevent cravings?

Naltrexone’s craving reduction lasts for as long as the effects of it do—about one day for the oral formulation and about one month for the injectable version, Vivitrol.

What should I avoid taking while on naltrexone?

Illicit substances, alcohol and some prescription medications interact. Don’t mix while taking naltrexone.

Reviewed By Peter Manza, PhD

Peter Manza, PhD received his BA in Psychology and Biology from the University of Rochester and his PhD in Integrative Neuroscience at Stony Brook University. He is currently working as a research scientist in Washington, DC. His research focuses on the role ... Read More

  1. Naltrexone. Treasure Island (FL): StatPearls Publishing. May 2023. Accessed May 2023.
  2. Vivitrol Prescribing Information. U.S. Food and Drug Administration. October, 2010. Accessed June 28, 2023.
  3. Revia Prescribing Information. U.S. Food and Drug Administration.. . October 2013. Accessed June 28, 2023.
  4. Half Life. Treasure Island (FL): StatPearls Publishing. . June, 2022. Accessed June 2023.

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