Quick Answer: Common naltrexone side effects include nausea, headaches, dizziness, fatigue, and difficulty sleeping, especially when starting treatment. Many mild symptoms improve with time, but signs of liver problems, severe allergic reactions, worsening mood, or sudden opioid withdrawal require medical attention.

Starting naltrexone can come with some uncertainty, especially when you’re also adjusting to life without alcohol or opioids. Nausea, fatigue, or trouble sleeping can make it difficult to tell what’s causing your symptoms, so understanding what’s common and when to contact your treatment team can help.

This guide focuses on naltrexone prescribed for alcohol or opioid use disorder, rather than low-dose naltrexone or weight-loss medications containing naltrexone. If you have questions about addiction treatment, talk with Wise Path Recovery Centers or call 866-860-9772 to explore your options.

What Are the Most Common Side Effects of Naltrexone?

The most common side effects of naltrexone involve digestion, energy levels, sleep, and general physical comfort. Some people experience only mild symptoms, while others find the first days of treatment more uncomfortable.

Here’s what people most often notice: 

• Nausea and stomach discomfort: Feeling sick, stomach cramps, vomiting, or loss of appetite.
• Headaches and dizziness: Head pain, lightheadedness, or feeling unsteady.
• Fatigue and drowsiness: Feeling unusually tired or noticing changes in your energy.
• Sleep disturbances: Difficulty falling asleep, staying asleep, or feeling rested.
• Anxiety and mood changes: Nervousness, irritability, restlessness, or emotional sensitivity.
• Muscle and joint pain: Aches or soreness that may affect everyday comfort.

Not everything you feel in early recovery comes from the medication. If you’ve recently stopped drinking, our guide on whether naltrexone helps with alcohol withdrawal explains how to tell the two apart. 

How Long Do Naltrexone Side Effects Last?

Mild naltrexone side effects often improve as your body adjusts to treatment, sometimes within the first several days or weeks. However, there’s no fixed timeline, and some people experience symptoms that persist or become difficult to manage.

How you feel matters more than reaching a specific day of treatment. Occasional nausea that gradually improves differs from vomiting that keeps you from eating, dizziness that interferes with work, or poor sleep that leaves you exhausted. Your prescriber should know when symptoms begin affecting your ability to function or participate in treatment.

If you’re struggling with side effects, keep track of when they happen, how long they last, and how they relate to your medication schedule. Include changes in appetite, sleep, and energy, along with any other medications you’re taking. These details can help your healthcare provider decide whether your symptoms need further evaluation or a treatment adjustment.

Don’t change your dose or stop taking naltrexone without speaking with your prescriber, unless you’re experiencing a serious reaction that requires immediate medical care.

How Can You Reduce Nausea From Naltrexone?

Naltrexone nausea is a common concern when beginning treatment, and it may be more noticeable if your appetite is already affected by early recovery. Taking oral naltrexone with a meal or a snack, rather than on an empty stomach, helps many people tolerate it better.

If nausea continues or makes it difficult to eat, your prescriber can review possible causes and determine whether a treatment adjustment is appropriate. Persistent vomiting, difficulty keeping fluids down, or signs of dehydration deserve prompt medical attention rather than waiting for your body to adjust.

Headaches can also make the adjustment period uncomfortable. Before taking an over-the-counter pain reliever, ask your prescriber or pharmacist which options are appropriate for you, especially if you have liver problems or a history of heavy alcohol use.

Does Vivitrol Have Different Side Effects Than Naltrexone Pills?

Yes. Oral naltrexone and Vivitrol contain the same active medication, but how they’re administered affects the side effects and how clinicians can respond. With daily tablets, the medication leaves your system fairly quickly, so if side effects become hard to manage, your prescriber can adjust the plan without much delay. 

Vivitrol is an extended-release injection that a healthcare professional generally administers once a month. It can cause many of the same general symptoms as oral naltrexone, along with injection-site reactions such as soreness, swelling, itching, bruising, or a lump.

Most injection-site discomfort is not severe, but some reactions can become serious. The official Vivitrol prescribing information describes cases of tissue damage and infection that have required surgery. If pain increases, swelling is substantial, blisters develop, or skin changes don’t improve, evaluate promptly.

Another difference is that Vivitrol remains active for approximately a month after injection and cannot simply be removed if side effects develop. For this reason, clinicians must carefully review a patient’s health and recent medication use before administering it.

Wise Path includes Vivitrol in its medication-assisted treatment program. The appropriate medication and treatment approach depend on each person’s clinical needs.

When Should You Worry About Naltrexone Side Effects?

Some discomfort may improve during the adjustment period, but certain symptoms need prompt evaluation. Knowing which reactions are more serious can help you recognize when routine follow-up is no longer enough.

Possible Liver Problems

Naltrexone can be associated with liver injury. Warning signs include yellowing of the skin or eyes, dark urine, pale stools, unusual fatigue, or persistent pain in the upper-right abdomen. Contact your healthcare provider immediately if you develop these symptoms. Your prescriber may also order blood tests to evaluate liver health before or during treatment.

Sudden Opioid Withdrawal

Naltrexone blocks opioid receptors and can trigger abrupt, potentially severe withdrawal if someone is physically dependent on opioids when treatment begins. Symptoms may include intense nausea, vomiting, diarrhea, sweating, agitation, and abdominal pain. Severe cases can require hospitalization.

This risk applies even when someone is taking naltrexone for alcohol use disorder. Tell your prescriber about all recent opioid use, including prescription pain medications, methadone, buprenorphine, and opioid-containing cough or diarrhea medications.

Severe Allergic Reactions

Swelling of the face, lips, or throat, difficulty breathing, or signs of a severe allergic reaction require emergency medical attention. Call 911 if these symptoms occur.

New or Worsening Depression

Changes in mood deserve attention during addiction treatment, particularly if someone develops worsening depression, hopelessness, or thoughts of self-harm. Tell your treatment provider about mood changes. If you’re experiencing suicidal thoughts or emotional distress, you can call or text 988 for immediate crisis support in the United States. Call 911 if there’s immediate danger.

Unusual Breathing Problems After Vivitrol

A rare condition called eosinophilic pneumonia has been reported in people receiving Vivitrol. Symptoms may include progressive shortness of breath or other pneumonia-like symptoms. Seek medical attention immediately for new or worsening breathing difficulties. Clinicians may also consider this condition when pneumonia symptoms don’t respond to antibiotics.

These reactions are uncommon, but they’re important reasons to stay in touch with your prescriber. You should also tell your care team about any unexplained naltrexone side effects that appear after beginning treatment, even if they aren’t listed here.

Finding the Right Support While You Adjust to Naltrexone

Finding the right medication can take some patience, and an uncomfortable first week doesn’t mean naltrexone is wrong for you. What helps most is having people in your corner who check in, listen to how you’re really feeling, and adjust the plan with you instead of leaving you to tough it out alone.

Wise Path’s medication-assisted treatment pairs naltrexone or other medications with counseling and medical support at our West Virginia locations. If you’re thinking about treatment or have questions about how medication might fit into your recovery, our team is here to talk it through.

FAQs About Naltrexone Side Effects