How Long Does It Take Naltrexone to Work?

More than 1 in 6 Americans struggle with substance misuse. Like other chronic conditions, substance use disorders are treatable, often with medication.

Naltrexone is one medication option that treats opioid use disorder (OUD) and alcohol use disorder (AUD). It comes as a once-daily oral tablet and a once-monthly injection called Vivitrol.

When starting medication for OUD or AUD, it’s best if it works quickly. But how long does it take naltrexone to work? And how long do you need to take it? We’ll answer these questions and more.

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How long does naltrexone take to work?

How long naltrexone takes to work depends on which form you’re taking. Each form of naltrexone is absorbed differently.

If you take naltrexone by mouth, it gets absorbed and starts working within an hour. The intramuscular (IM) injection takes a little longer to start working — about 2 hours. Full effects from the IM injection may take a few days.

Once naltrexone starts working, it helps decrease alcohol and opioid cravings. This is because  naltrexone is an opioid blocker. It blocks opioid receptors (binding sites) in the body. This decreases the levels of two substances in the body: natural opioid substances and a chemical called dopamine. This makes opioids and alcohol less enjoyable, reducing cravings for them.

How do you know if naltrexone is working?

If you experience fewer opioid or alcohol cravings after starting naltrexone, it’s working. Keep in mind, recovery from substance use disorders is a lifelong process. And how long it takes to stop using a substance varies from person to person. If your recovery isn’t progressing as you’d like, talk to your prescriber. They may suggest adding or changing treatments.

Naltrexone isn’t considered the most effective medication for OUD. It helps with opioid cravings, but it doesn’t treat opioid withdrawal symptoms. Instead, first-choice medications like buprenorphine, buprenorphine / naloxone (Suboxone, Zubsolv), and methadone (Methadose) are better options for most people. They’re more likely to help you quit opioids and prevent overdose.

But naltrexone still may be a good option for some people, especially those who can’t — or don’t want to — take methadone or a buprenorphine-containing medication. If naltrexone is used for OUD, the injection is the preferred form.

EXPERT PICKS: WHAT TO READ NEXT

• Naltrexone side effects to watch for: Naltrexone side effects, such as nausea and headache, are usually mild. But rarely, severe risks like liver damage can occur.

• Comparing medications for opioid use disorder (OUD): When looking at different medications that treat OUD, naltrexone isn’t always the best choice.

• Comparing medications for alcohol use disorder (AUD): There are a few medication options for AUD. The best choice for you depends on several factors.

On the other hand, naltrexone is a first-choice medication for AUD. It can help you quit or reduce your drinking, depending on your goals. Either form is a reasonable option for AUD.

Are there factors that can affect how long naltrexone takes to work?

If your goal is to quit opioids or alcohol, taking your naltrexone doses consistently can help you experience its effects more quickly. Not taking it consistently makes it more likely for opioid or alcohol cravings to surface, increasing your chance of returning to substance use.

If you prefer to avoid taking an oral medication daily, the naltrexone injection may be a better option. The injection must be given by a healthcare professional every 4 weeks, often at the clinic where you’re receiving treatment. So make sure to keep up with your appointments to get the most out of naltrexone.

It’s important to note that some people don’t take naltrexone tablets every day. In some cases, naltrexone is prescribed to help reduce binge drinking. This is referred to as “targeted naltrexone” therapy. If you think you may be tempted to drink too much before an event, you can take oral naltrexone. This is instead of taking naltrexone on a daily basis.

Using other nonmedication treatments along with naltrexone can help boost your chances of successfully quitting opioids or alcohol. This includes engaging in talk therapy or support groups.

Everyone has a different recovery process. If naltrexone doesn’t seem to be working for you, tell your prescriber. They may suggest trying another medication.

What to expect when starting naltrexone

Below, we discuss several important points to remember before starting naltrexone.

Tell healthcare professionals that you’re using naltrexone

Naltrexone can block opioid effects. If you’re in an emergency situation that requires pain medications, tell the emergency healthcare professionals that you’re taking naltrexone. Keeping a patient safety card on your person is one way to do this. This will help them come up with a plan to best manage your pain.

You can usually manage side effects at home

Naltrexone has been used to treat substance use disorders for 40 years. This long track record shows that naltrexone is usually well-tolerated. But like all medications, naltrexone side effects can still occur.

Common side effects like nausea, headaches, and dizziness are usually mild and improve within a few days. With the IM injection, injection site reactions include mild redness, itching, and swelling.

Rarely, liver damage can occur. So if you experience symptoms like swelling in the abdominal area, jaundice (yellow skin or eyes), or dark-colored urine, seek emergency care.

You might need to wait before starting naltrexone

Naltrexone strongly attaches to opioid receptors. In fact, it binds so strongly that it can bump off typical opioids that are bound to these receptors. So if any opioids are in your system when you start naltrexone, uncomfortable opioid withdrawal symptoms can occur since their effects are quickly blocked.

After you stop opioids, a 7- to 10-day waiting period may be recommended before starting naltrexone. But if you’re being closely monitored, your care team might recommend starting naltrexone sooner. In some cases, your prescriber may test your blood to make sure opioids are fully out of your system.

There are other treatment options if naltrexone doesn’t work

If naltrexone doesn’t seem to be helping you — or is causing bothersome side effects — tell your healthcare team. They may suggest switching to another medication or recommend additional treatment options. For example, many people with substance use disorders also have mood disorders, like anxiety or depression. So they might recommend additional medications or treatment options to improve these conditions.

If your prescriber recommends switching you to methadone or Suboxone for OUD, you can start either of these as soon as the majority of your last naltrexone dose is cleared from your body. This is typically about 1 day after naltrexone tablets or 30 days after the injectable form.

Be aware of overdose risk after starting naltrexone

Your body loses tolerance to opioids after you stop taking them. This can make you more sensitive to opioid effects if you return to opioid use. This is especially true if you take more opioids to try to overcome naltrexone’s opioid-blocking effects.

Returning to opioid use after using naltrexone can result in a life-threatening opioid overdose. That’s why it’s important to speak with your prescriber immediately if you feel you’re at risk for relapse or if you’ve already relapsed. They can offer support and talk about how to proceed.

Good to know: Other opioid blockers called naloxone (Narcan, Zimhi) and nalmefene (Opvee, Zurnai) are used to quickly reverse the effects of an opioid overdose. But naltrexone doesn’t have the same effect. It shouldn’t be used in an emergency overdose situation. Since relapse is often part of the recovery process, always keep a naloxone or nalmefene medication on hand if you’re diagnosed with OUD. Naloxone nasal spray can be found over the counter. You can also get a prescription from your prescriber. Injectable naloxone and nalmefene are available with a prescription.

How long do you need to take naltrexone?

There’s no universal recommendation for how long you’ll need to take naltrexone for AUD and OUD. Studies of naltrexone for AUD and OUD typically last 3 to 12 months. But the optimal length of treatment will depend on how severe your condition is, your personal preferences, and whether naltrexone is causing any side effects. Treatment for AUD and OUD is often a long-term process. And some people may take naltrexone indefinitely.

There’s no risk of naltrexone withdrawal if you stop taking it abruptly, but you should talk to your care team first if you’re interested in stopping naltrexone. They can help you come up with a plan to make sure you have adequate support in place before you stop it. This decreases your risk of returning to alcohol or opioid use.

Why trust our experts?

Written by:

Daphne Berryhill, RPh

Daphne Berryhill, RPh, has two decades of experience as a clinical pharmacist. She spent most of her career in the Chicago area practicing in-home infusion.

Edited by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

Reviewed by:

Jonathan Avery, MD

Jonathan Avery, MD, is the current vice chair of addiction psychiatry and an associate professor of clinical psychiatry at Weill Cornell Medical College and New York-Presbyterian Hospital.

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