Naltrexone can be used as part of a medication-assisted treatment plan for opioid use disorder (OUD), as well as alcohol use disorder.

While every medication can cause side effects, including naltrexone, the good news is that most side effects are mild and get better as your body adjusts to the medication. Understanding what to expect and when to contact your healthcare provider can help you manage side effects and stay on track with recovery.

How Naltrexone Works

Unlike other medications frequently used to treat OUD, naltrexone doesn’t activate opioid receptors.

Instead, it’s an opioid antagonist, which means it blocks opioid receptors in the brain. It also blocks the effects of endorphins, the body’s natural “feel-good” chemicals that create feelings of pleasure.

By blocking opioid receptors, naltrexone can reduce opioid cravings and stop opioids from producing a high if they’re taken. It also makes drinking alcohol feel less rewarding. As a result, many people find it easier to avoid drinking or using opioids while using this treatment.

Why Side Effects Are Often Worse at the Beginning

During the first weeks of taking naltrexone, your brain and body are getting used to blocked opioid receptors. This explains many of the side effects you may have and why they may happen early on.

If a person starts naltrexone too soon after the last time they used opioids, it may cause sudden withdrawal symptoms. To avoid this, your body needs time to fully clear the opioids you’ve taken before starting naltrexone.

Most people will need to wait at least seven to 10 days after using a short-acting opioid, like oxycodone or fentanyl. If you’re taking a long-acting opioid — such as methadone, buprenorphine or extended-release forms of opioids — you’ll need to wait at least 10 to 14 days after your last dose. This is to prevent severe opioid withdrawal.

Your healthcare provider may use a urine drug test to make sure opioids have cleared from your body. In some cases, they may also give a naloxone challenge. This is when they give you a small dose of naloxone, an opioid antagonist, to check if opioids are still in your system.

What Can Help With Naltrexone Side Effects

If you find yourself taking naltrexone and having side effects, there are some things you can do to help manage them.

Some ways to help reduce side effects are:

• Being opioid-free for the recommended time before starting treatment
• Starting a lower dose and increasing it slowly over time
• Taking naltrexone with or after meals

If you’re taking oral naltrexone and side effects are too bothersome for you, your healthcare provider may consider reducing the dose for a short period of time before increasing it again. It’s important not to change your dose or stop taking naltrexone without talking to your doctor first.

Although most people only experience mild side effects, it’s important to know when side effects may be serious and require medical attention.

Other Important Facts To Remember

Avoid using opioids while taking naltrexone. Because naltrexone blocks opioid receptors, opioid medications will not work as well.

If you need pain treatment for emergency medical care, tell your healthcare team you’re taking naltrexone so they can choose the safest treatment for you.

It’s important not to try to overcome naltrexone’s blocking effects by taking more opioids. This can increase your risk of an overdose. If you have concerns, your healthcare team can help you stay safe and answer any questions you have about your treatment.

Join the Conversation

On MyOpioidRecoveryTeam, people share their experiences with opioid use disorder, get advice, and find support from others who understand.

Did you have any side effects when taking naltrexone, and what helped you manage them? Let others know in the comments below.