Last Updated on August 4, 2025

💡 This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider before starting, stopping, or changing any medication or treatment plan, including the use of naltrexone. Individual needs and responses to treatment can vary.

The FDA-approved prescription medication naltrexone can be an excellent resource for people who wants to drink less, especially for folks seeking balance and moderation. The research is incredibly promising, especially when combined with a science-backed behavior-change program like Sunnyside.

Naltrexone is usually well-tolerated. But, as with most medications, you might experience some side effects when you first start taking it. It’s helpful to be aware of those side effects up front, so you can have the most comfortable experience possible.

How Naltrexone Works

Naltrexone basically works by blocking opioid receptors in your brain. This dulls alcohol’s “rewarding” effects and can make it seem less appealing over time. This means fewer cravings, less alcohol consumption overall, less binge drinking, and an overall healthier lifestyle.

The medication comes in two forms: a daily oral tablet and a monthly injectable. The latter is also known as Vivitrol.

Is Naltrexone Safe?

Naltrexone is well-tolerated by most people. Everyone should talk to a medical professional before taking Naltrexone, and certain groups of people should be particularly cautious.

• People with liver issues
• People with opioid use disorder
• People who are pregnant
• People who are breastfeeding

Most Common Naltrexone Side Effects

Some naltrexone side effects occur in many new users and typically dissipate pretty quickly. Frequently reported naltrexone side effects include:

• Gastrointestinal discomfort like nausea, stomach cramps, diarrhea, or vomiting
  
• Headache, dizziness, and fatigue, especially when beginning the oral medication
  
• Sleep issues such as insomnia, newly vivid or bizarre dreams, anxiety, or irritability in the morning
  
• Muscle or joint problems like aches, cramps, or stiffness.
  

With the injectable Vivitrol, you may experience reactions at the injection site, including redness, soreness, swelling, and/or bruising. These often improve on their own within days. If symptoms persist for more than two weeks or become excessively bothersome, consult your healthcare provider.

Managing Common Oral Naltrexone Side Effects

Here are practical tips to make the side effects of oral naltrexone more manageable:

• Take oral naltrexone with food. It’s best to take oral naltrexone with a light snack. This can ease nausea.
  
• Be sure to drink plenty of water throughout the day. Dehydration can exacerbate side effects such as dizziness or headache.
  
• Take your first dose of naltrexone after completing your daily responsibilities. For most people, this means taking it in the evening. This will ensure that any side effects don’t interfere with your work or family life, allowing you to focus on how you’re feeling and how best to manage any symptoms. 
  
• Ensure you follow your doctor’s titration recommendations, which typically start with a half dose (25mg) for the first 7 days, and increasing to a full dose on day 8. If you’re extra sensitive to the naltrexone, you might even start at a lower dose.
  

Serious (But Rare) Naltrexone Side Effects to Be Aware Of

Naltrexone can also have more serious side effects. Don’t worry: These are much less common. Still, it’s good to be aware of them. Contact your healthcare provider if you experience any of them.

• Liver issues: High doses of naltrexone may impact liver function. Especially if you have a history of liver problems, your doctor may recommend regular liver enzyme tests.
  
• Mood changes: This includes depression, suicidal ideation, or worsening anxiety. If you notice mental health symptoms that cause you alarm, seek support immediately.
  
• Allergic reactions: Swelling of the face or throat, severe rash, or breathing difficulty are emergencies.
  
• Opioid withdrawal: If naltrexone is taken while opioids are in your system, which is inadvisable, it can cause sudden withdrawal reactions like sweating, vomiting, diarrhea, agitation, or hallucinations.

• Eosinophilic pneumonia is a type of pneumonia caused by excessive levels of eosinophils, a type of white blood cell.

Contact Your Doctor Immediately If…

Most side effects are predictable and go away fast—no cause for panic! But you should contact your doctor if:

• You have dark urine, yellowish skin, or severe upper-right belly pains (these are symptoms of liver stress)
• You feel persistently depressed or are considering self-harm
• You notice signs of an allergic reaction, such as swelling or a rash
• You have difficulty breathing
• You experience severe vomiting or diarrhea, especially if you’re also feeling dizzy and/or dehydrated

These symptoms constitute emergencies and should be addressed ASAP.

It’s important to understand Naltrexone’s side effects

Naltrexone can be a life-changing tool. Knowing what side effects might come up can help you feel more grounded and in control as you change your relationship with alcohol.

For most people, naltrexone side effects are manageable. And with awareness and clear communication with your medical provider, naltrexone can be a helpful tool in moderating alcohol without relying solely on willpower.

Want to learn more? Check out our full Naltrexone 101 guide to learn more about adding naltrexone to your mindful drinking toolkit.

What is Sunnyside?

Sunnyside is a mindful drinking and alcohol moderation app that can help change your habits around alcohol using a proven, science-backed method. Whether you want to become a more mindful drinker, drink less, or eventually quit drinking, Sunnyside can help you reach your goals. We take a positive, friendly approach to habit change, so you never feel judged or pressured to quit.

When you join Sunnyside, you’ll start by completing a 3-minute private assessment so we can learn a bit about you. Once that’s done, you’ll get a 15-day free trial to test out everything, including our daily habit change tools, tracking and analytics, community and coaching, and education and resources. It’s a full package designed specifically to adapt to your goals and help you reach them gradually, so you can make a huge impact on your health and well-being.

Sunnyside is a digital habit and behavior-change program that is incredibly effective on its own, but can also be the perfect complement to other work you’re doing to cut down on drinking, whether that includes talk therapy or medication such as Naltrexone.

Get your 15-day free trial of Sunnyside today, and start living your healthiest life.