How Long Does Naltrexone Take to Work?

Medically Reviewed by
Vanessa de la Cruz, MD
February 14, 2022

Naltrexone, sold under brand names such as ReVia, Vivitrol, and Depade, are medications for opioid use disorder (MOUD) and alcohol use disorder (AUD). Naltrexone was initially approved by the U.S. Food and Drug Administration (FDA) in 1984 to treat opioid addictions such as heroin, morphine, and oxycodone. And it was later approved for treating alcohol use disorder in 1994. 

Naltrexone is available as a daily dose in a pill form (ReVia and Depade) or as a monthly intramuscular injection (Vivitrol) for treating alcohol and opioid use disorders. Naltrexone is considered unique to other substance use disorder medications because it treats both opioid and alcohol use disorders. When used in combination with behavioral therapy, counseling, and aftercare support, naltrexone is a highly effective medication.

How Does Naltrexone Work?

Naltrexone belongs to a class of medication known as an opioid antagonist (inhibitors). Naltrexone works by blocking the sedative and intoxicating effects of opioids by binding to the endorphin receptors in the body and blocking opioid receptors in the brain. This function helps maintain abstinence and prolong recovery. Naltrexone is effective in substance use disorder maintenance treatment because it’s a non-narcotic medication with a low risk of misuse. Naltrexone can be prescribed and administered by any practitioner licensed to prescribe medications since it is not a controlled medication. 

Individuals must remain opioid-free for at least seven days after their last use of short-acting opioids and 10-14 days after their last use of long-acting opioids before initiating naltrexone treatment to lessen the risk of rapid opioid withdrawal syndrome. Naltrexone can be prescribed to those who are currently using alcohol. While naltrexone does not necessarily stop you from drinking or reverse the intoxicating effects of alcohol, it does gradually reduce the amount that you drink. However, it may take many weeks after starting naltrexone to notice a reduction in opioid or alcohol cravings. 

How Long Does It Take For Naltrexone to Work?

Oral naltrexone absorbs quickly and begins to work within an hour after consumption. The effects of the 50-mg oral tablet can last for 24 to 36 hours. The duration of higher doses is longer lasting, with 100 mg lasting 48 hours and 150 mg lasting 72 hours. Naltrexone usually reaches its peak within one hour of dosing.

The dosing of intramuscular extended-release naltrexone (Vivitrol) is 380 mg given as a monthly injection. Vivitrol reaches its initial peak around two hours after administration, followed by a second peak within two to three days. Two weeks after administration, the medication’s concentration in the body begins to decline. It can, however, be detected for up to 50 days after initial administration.

Possible Side Effects of Naltrexone

In addition to its beneficial effects, naltrexone can also cause certain negative effects. However, the majority of these side effects are minor and fade away with time.

Common side effects of naltrexone include:

  • Headache
  • Nausea
  • Vomiting
  • Diarrhea
  • Loss of appetite
  • Muscle or joint pain
  • Constipation
  • Dizziness
  • Irritability
  • Insomnia 
  • Nervousness
  • Abdominal pain
  • Toothache
  • Cold symptoms

Naltrexone can cause severe side effects in rare circumstances. These side effects may include:

  • Severe injection site reactions 
  • Depressed mood
  • Pneumonia
  • Risk of liver damage or hepatitis
  • Blurred vision
  • Hallucinations
  • Pneumonia
  • Serious allergic reactions such as skin rash, wheezing, and chest pain

Medical professionals advise that you discuss the following conditions with your healthcare provider before starting naltrexone treatment to lessen the chance of side effects. These conditions include:

  • Health conditions such as kidney and liver damage, hemophilia, or other bleeding problems.
  • Allergic to naltrexone, including any of the ingredients or the liquid used to mix the extended-release naltrexone.
  • Presently using any other form of illicit substances.
  • Medications currently in use, including prescriptions and non-prescription medicines, herbal supplements, and vitamins.
  • If you are pregnant, planning to become pregnant, or breastfeeding. 

Your healthcare practitioner can determine the safest dose of naltrexone or recommend an alternative medicine based on these conditions.

How Long Does Naltrexone Stay In Your System? 

Determining exactly how long naltrexone is detectable in your body depends on many variables. These variables include the form of naltrexone taken and the type of drug tests being utilized.

The timetable for detecting naltrexone in the body also depends upon factors such as:

  • Metabolism
  • Body mass
  • Age
  • Hydration level
  • Physical activity
  • Health conditions

These variables make it almost impossible to determine an exact time naltrexone will show up on a drug test. However, naltrexone is usually detected in the urine within the first four to six hours following administration and for up to 24 hours in the blood and saliva. And it can also be detected in the hair for up to 90 days. Vivitrol, on the other hand, can remain detectable in drug tests for months.

Typically, for a drug test to detect a certain substance, that substance must be specifically tested. And naltrexone is not generally included in any of the typical testing panels. 

Interactions With Other Medications

Naltrexone may interact with other medications, resulting in severe side effects. Since this medication is used to treat alcohol and opioid addiction, individuals on naltrexone must avoid certain medications to prevent unpleasant withdrawal symptoms. Before starting naltrexone, inform your healthcare provider of any other medications you’re taking, including over-the-counter medicines and herbal remedies.

Medications that interact negatively with naltrexone include:

  • Narcotic medications, such as codeine and hydrocodone
  • Diarrhea medications
  • Disulfiram
  • Cough medication

Is It Possible to Overdose on Naltrexone?

It’s theoretically possible to overdose while on naltrexone if a person takes large amounts of opioids or alcohol in an attempt to counteract the effects of naltrexone or in case of a relapse after a period of maintained abstinence. 

Signs and symptoms of an overdose include:

  • Nausea
  • Stomach pain
  • Dizziness
  • Seizures or convulsions

Opioid overdose is a medical emergency that requires immediate medical attention. 

Naltrexone is a non-narcotic medication with a low risk of side effects. However, naltrexone works best when combined with other aspects of SUD treatment, such as behavioral therapy, counseling, and aftercare support. 

If you are seeking help with your loved one’s addiction, contact us today or complete our quick contact form below, to speak with an addiction treatment specialist.

If you need help with your substance use disorder, we are here to help you build your confidence and momentum towards the future you want. We provide treatment services for adults with alcohol, opioid, and other substance use disorders. We are currently located in Florida, LouisianaMassachusettsNew JerseyNorth CarolinaOhio, Texas, and Washington.

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Vanessa de la Cruz, MD

Dr. de la Cruz is an Adult Psychiatrist and is also certified in Addiction Medicine. She has experience treating anxiety, depression, psychosis, personality disorders, and substance use disorders via medication management (including buprenorphine) and therapy. She employs an evidence-based, trauma focused approach and has experience in developing integrated care programs.

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