Naltrexone Half-Life. How Long Does It Stay In One’s System?

Last Updated: June 24, 2020

Authored by Olivier George, Ph.D.

Reviewed by Michael Espelin APRN

When first starting the drug, many patients wonder how long Vivitrol stays in their system, how it works, and whether it is right for them. Depending on the formulation, naltrexone half-life may vary from several hours to several days. Many factors determine the concrete time of how long the drug stays in their system.

Naltrexone Half-Life

The half-life of naltrexone strongly depends on how the medication is delivered. Oral naltrexone HCL is metabolized to 6-β-naltrexol, its primary active metabolite. 6-β-naltrexol has a half-life of 13 hours. This way, a patient only has to take one ReVia 50 mg pill daily to achieve sufficient and stable concentrations of the medication.

At the same time, the half-life of Vivitrol (an injectable form of the medication) is 5-10 days. Injectable naltrexone provides a steady release of the drug into the person’s system that lasts for approximately a month. The extended Vivitrol half-life is particularly convenient for patients who don’t wish to pop a pill daily for a significant period of time.

How Long Does Naltrexone Stay In The System?

The time during which the medication stays active or, at least, detectable in a person’s system is determined by Vivitrol dosing and the way of administration. When the drug is injected, it is active in a patient’s system for a month. Oral naltrexone has to be consumed daily.

Naltrexone In Blood System

Oral naltrexone can be detected in blood for up to 24 hours after a person took the last dose. The elimination might take longer if the patient is older or has a slower metabolism. Also, trace amounts of the medication can be present in a person’s system for as long as 3-4 days after the last 50 mg dose was ingested.

Naltrexone In Urinary System

The drug can be detected in urine for 4 to 6 hours after it was consumed. However, it does not mean that the medication stops working after this period. Naltrexone stays in the system and continues to exert influence long after it becomes undetectable in the urine. It is an important thing to remember when an interaction between Vivitrol and alcohol or other substances needs to be considered.

how long does vivitrol stay in saliva

Naltrexone In Saliva

A saliva test can help detect Vivitrol 24 hours after a person took the last dose.

Naltrexone In Hair

Vivitrol stays in hair follicles for the longest. It can be detected for approximately 90 days after a person took the last dose of the medicine.

Metabolism Of Naltrexone

Naltrexone mechanism of action relies on the drug’s ability to bind to opioid receptors in the body without inducing euphoria. When the drug is injected, it is released into blood plasma in phases. The initial release of the medicine from polymer microspheres that contain it occurs in 24 hours after the injection. Subsequently, the extended Vivitrol half-life and the gradual erosion of the polymer microspheres allow the medication to be released effectively into a person’s system for a month after the injection.

Naltrexone On A Drug Test

Many patients have concerns about whether Vivitrol shows up on a drug test. A standard drug screen that is used to detect opioid drugs or other controlled substances in a person’s system will not detect Vivitrol. A special naltrexone drug test is required to discover the medication.

Will Low-Dose Naltrexone Show Up On A Drug Test?

Low-dose naltrexone only shows up on tests that are specifically designed to detect this medication. Since one cannot get high on Vivitrol, it is not a controlled substance. The testing, therefore, is not likely to be required by an employer or in any other non-medical setting. Those who seek how to flush naltrexone out of their system quickly should remember that it brings no benefits, and sudden discontinuation of the treatment can lead to a relapse.

does naltrexone show up in drug test

Will Vivitrol Test Positive For Opiates?

Naltrexone false positive urine drug test result is a big concern for many patients who take the medication. Some begin wondering how to get Vivitrol out of their system before the test date. This is not only unnecessary but potentially extremely dangerous.

Vivitrol isn’t known to cause a false positive result on a drug test for opiates. If the result comes positive, the individual can request to run the test again.

Stay Aware Of Naltrexone In The System

Due to a relatively long half-life, naltrexone stays in a person’s system for more than a day in pill form and a month when given as an injection. The remnants of oral naltrexone can be found in blood 24 hours after the last dose of the drug was administered and for as long as 90 days in hair follicles. For those who are involved in drug abuse, addiction treatment is needed. The help can be found in the professional rehabs. It’s always better to stay under supervision to prevent relapse.

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Published on: June 7th, 2019

Updated on: June 24th, 2020

About Author

Olivier George, Ph.D.

Olivier George is a medical writer and head manager of the rehab center in California. He spends a lot of time in collecting and analyzing the traditional approaches for substance abuse treatment and assessing their efficiency.

Medically Reviewed by

Michael Espelin APRN

8 years of nursing experience in wide variety of behavioral and addition settings that include adult inpatient and outpatient mental health services with substance use disorders, and geriatric long-term care and hospice care.  He has a particular interest in psychopharmacology, nutritional psychiatry, and alternative treatment options involving particular vitamins, dietary supplements, and administering auricular acupuncture.


Leave a comment

  • Sandy Howatt
    Do you have any information on false positives while on Vivitrol with a drug patch (Pharchek) ?
  • Sandra sobel
    Taking low dose neltrexone For a antiflamorty for two weeks iit finally has made me sick Nausea so fatigued can not Move i must stop this drug.