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How Long Does Naltrexone Take to Work?

July 6, 2022

Table of Contents

Naltrexone comes in two forms: a pill and an injection. How long naltrexone takes to work depends on the form of the prescription you're using.

Injectable naltrexone starts working almost immediately and reaches peak concentrations in your blood about two hours after your shot.[1]

Oral naltrexone starts working about an hour after you take it.[2] The drug must move through your digestive tract, so it comes on a little slower than an injection. 

How Long Does Naltrexone Last?

Oral Naltrexone lasts to prevent cravings in your body for alcohol for about a 24 hour period. It is for this reason that it is dosed once a day.

Naltrexone injections last in the body for about a month at a time.[3]

Every person’s body is different, and some people feel the impact of naltrexone faster, and they metabolize the prescription sooner too.

How quickly you'll process naltrexone depends on the following:

  • Your age
  • Your height and weight
  • Your organ health 
  • Your personal genetics 
  • The severity of your cravings for alcohol

If you're using naltrexone and you feel it's wearing off too quickly or not covering cravings later in the day, talk with your doctor. You could need a dose adjustment to get the most effectiveness out of your medication. 

Naltrexone Timing FAQs

Does naltrexone work the first day?

Yes, both oral and injectable naltrexone start working in the body the first day they are used.

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

Injectable naltrexone starts working almost immediately and reaches peak concentrations in your blood about two hours after your shot.[1] Oral naltrexone starts working about an hour after you take it.[2] The drug must move through your digestive tract, so it comes on a little slower than an injection.

Elena Hill, MD, MPH

Elena Hill, MD; MPH received her MD and Masters of Public Health degrees at Tufts Medical School and completed her family medicine residency at Boston Medical Center. She is currently an attending physician at Bronxcare Health Systems in the Bronx, NY where she works as a primary care physician as well as part time in pain management and integrated health. Her clinical interests include underserved health care, chronic pain and integrated/alternative health.

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Citations

  1. Chapter 5: Extended Release Injectable Naltrexone. Incorporating Alcohol Pharmacotherapies Into Medical Practice. https://www.ncbi.nlm.nih.gov/books/NBK64031/. 2009. Accessed June 2022.
  2. Chapter 4: Oral Naltrexone. Incorporating Alcohol Pharmacotherapies Into Medical Practice. https://www.ncbi.nlm.nih.gov/books/NBK64042/. 2009. Accessed June 2022. 
  3. Naltrexone Injection. U.S. National Library of Medicine. https://medlineplus.gov/druginfo/meds/a609007.html. November 2010. Accessed June 2022.

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