How Long Does Naltrexone Last?


After taking oral naltrexone treatment for alcohol or opioid use disorder, patients feel its effects for 24 to 72 hours. In the case of intramuscular extended-release naltrexone, its action is long-lasting – up to 28 days.

Naltrexone is an opioid antagonist used in substance abuse treatment. It works by blocking opioid receptors being triggered by stimulants like alcohol and illicit drugs. Its effects depend on the method of administration, which doctors determine after discussing with patients and assessing their overall condition.

How Long Does Naltrexone Stay in Your System?

Upon administration, naltrexone takes about an hour or two to act before patients can feel fewer cravings. How long these effects last depends on the drug form:

Oral Naltrexone

Oral formulation means taking naltrexone pills every day, every other day, or every third day. The doses in question are 50, 100, and 150 mg, respectively. As it’s a prescription medication, doctors determine the exact dosage for every patient, depending on their health condition and recovery treatment stage.

The drug’s half-life in pill form is four hours, meaning that four hours after taking a pill of 50 mg of naltrexone, its concentration in the blood drops to 25 mg. After another four hours, it goes to 12.5 mg, and so on. At that rate, naltrexone is eliminated from the body in one to three days at the most.

Naltrexone Injection

Another form of naltrexone treatment is the intramuscular injection. Patients get their dose (380 mg) once a month. Naltrexone is released in their systems over time, so they receive a steady dose over four weeks, keeping drug amounts at optimal levels to prevent opioid or alcohol cravings.

For the long-acting injectable formulation, naltrexone half-life is anywhere between five and ten days. After that, the amount of this opioid antagonist in the patient’s system drops, but full opioid-blocking effects still last. Following the general rule that it takes about five half-lives to eliminate any drug from the body, naltrexone injection effects will last about 28 days.

What Factors Affect Naltrexone Effects?

How long naltrexone stays in the patient’s body depends on several factors, besides the administration method:

  • Dosage: Higher naltrexone doses for treating alcohol or opioid addiction might have prolonged effects. For example, a single 50 mg pill will be effective for 24 hours, while a 150 mg dosage can last up to three days.
  • Patients’ age: As people get older, their metabolism rate slows down, meaning their bodies process naltrexone slower than younger patients.
  • Body weight: People with higher body mass index might have problems with naltrexone metabolism as fat deposits around organs can prevent them from processing this drug.
  • Organ health: If patients have liver issues, these can slow down naltrexone metabolism and absorption.

How Does Naltrexone Work?

Naltrexone blocks the effects of opioids, and it’s used to treat alcohol and opioid addiction. The purpose of this antagonist is to reduce the addict’s enjoyment of illicit substances by acting on opioid receptors.

This drug prevents their intoxicating and sedative effects (the feelings of being “high” and drowsy), which is why the patient’s urge for opioid drugs and alcohol consumption drops. Upon ingestion, the body uses only a certain amount of naltrexone while the liver processes the rest and eliminates it.

Naltrexone isn’t a cure for any form of opioid or alcohol addiction. The American Food and Drug Administration (FDA) has approved it as a pharmaceutical addition to the overall recovery treatment that should include detoxification, self-help groups, and counseling.

This opioid antagonist can help with drug and alcohol use disorders, but only if the doctors include it in the addiction treatment later. As this drug can trigger opioid withdrawal symptoms in people struggling with substance abuse, it should become part of the treatment once there’s no risk of relapse.

Who Can Take Naltrexone?

People who are currently drug- and alcohol-free for at least seven days can receive naltrexone as a part of medication-assisted treatment. It’ll help them stay sober and clean with no relapse.

On the list of what to avoid when taking naltrexone are all kinds of opioids, meaning the patient must be clean at least seven days before taking this drug. After finding no traces of opioids in the patient’s body, the doctor determines the treatment and can prescribe medications like naltrexone.

Frequently Asked Questions

How Long Is Naltrexone Detectable in the Body?

Naltrexone traces show up in urine for about four to six hours after ingestion. They can be detected in blood and saliva within 24 hours, while drug tests using hair follicles can find naltrexone traces up to three months after taking this drug.

Is Naltrexone Available with No Prescription?

No, naltrexone isn’t an over-the-counter medication. It’s a controlled substance by the American Food and Drug Administration for treating addiction, and it’s only available to patients after their doctors prescribe it.

Are There Any Side Effects of Naltrexone Use?

Naltrexone is effective in treating a substance use disorder since it has no addictive properties on its own. The risk of drug abuse in this case is almost non-existent, but there are some side effects of naltrexone to be noted.

Higher doses of naltrexone can cause a reaction at the injection site, sleep problems, skin rash, and chest pain, but these should pass in a couple of weeks at most. If these symptoms persist longer, patients should talk to their doctors.

Severe side effects of naltrexone treatment may include an allergic reaction, problems with the liver and gastrointestinal system, depression, nausea, and dizziness that lasts for a long time. If that happens or in case of accidental overdose, urgent medical help is necessary.

Final Thoughts

For people struggling with opioid or alcohol use disorder, naltrexone can be a solution. This drug’s effects depend on the method of administration and dosage, and when taken under medical supervision, it can greatly contribute to any recovery plan and prevent opioid relapse in the long run.


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