Last Updated on June 20, 2026
Naltrexone side effects are usually mild and temporary, most often including nausea, headache, dizziness, fatigue, sleep changes, and digestive discomfort. For most people, side effects are strongest during the first few days and improve within one to two weeks. While side effects often appear immediately, naltrexone’s benefits build over time, making adherence one of the biggest predictors of success for reducing cravings, heavy drinking days, and overall alcohol consumption.
Naltrexone is one of the most well-studied medications available for people who want to drink less. Whether your goal is moderation, abstinence, or simply getting out of a cycle of gray-area drinking, it’s FDA-approved (since 1994), non-addictive, and backed by decades of research showing it can reduce cravings, heavy drinking days, and overall alcohol consumption.
Like any medication, though, naltrexone can cause side effects.
The good news is that most naltrexone side effects are mild and temporary, and they improve as your body adjusts to the medication. Knowing what to expect can make the first few weeks easier and—together with support from Sunnyside Med—help you stay on naltrexone long enough to experience its benefits.
How Naltrexone Works
Naltrexone works by reducing the brain’s reward response to alcohol. Normally, alcohol triggers the release of endorphins, which activate opioid receptors and contribute to the pleasurable “reward” signal that reinforces drinking. Naltrexone dampens that response.
Over time, many people notice:
- Reduced cravings
- Less interest in alcohol
- Fewer heavy drinking episodes
- An easier time adhering to mindful drinking goals
“Drinking might feel different, and that’s the point. Less exciting. Less rewarding. Sometimes just… less fun,” says Sunnyside co-founder Ian Andersen. “That’s the medication doing its job.”
Research consistently supports these effects. In the landmark COMBINE study, one of the largest alcohol treatment studies ever conducted, participants taking naltrexone experienced significantly better drinking outcomes than those receiving a placebo, particularly when the medication was paired with behavioral support.
Naltrexone is available in two forms:
- Oral naltrexone tablets
- Monthly injectable naltrexone (Vivitrol)
Most people using naltrexone for alcohol reduction take the oral form. That’s what we offer at Sunnyside Med.
Is Naltrexone Safe?
For most people, yes.
A 2023 systematic review and meta-analysis published in JAMA analyzed 118 clinical trials involving more than 20,000 participants and found that oral naltrexone was generally safe and well-tolerated.
That said, you should definitely talk with a healthcare provider before taking it, especially if you:
- Use opioid medications
- Have acute hepatitis or severe liver disease
- Are pregnant or breastfeeding
- Have recently used opioids and may be at risk for withdrawal
Your clinician can help you determine whether naltrexone is appropriate for your situation.
The Most Common Naltrexone Side Effects
Nervous about side effects? That’s understandable when starting a new medication.
Naltrexone tends to be on the milder side when it comes to side effects, though they are definitely possible. Most side effects occur during the first few days or weeks of treatment and improve with time.
Nausea
Nausea is the most commonly reported side effect of oral naltrexone, affecting between 10-20% of patients. There’s a chance you might not experience it at all, but if you do, it’s likely to be relatively short-lived. For example, in one clinical trial conducted by Dr. Glenn-Milo Santos et al, all participants who experienced nausea while taking naltrexone found that it was “mild to moderate,” and that it resolved as they became used to the medication.
Some people notice mild stomach upset during their first several doses, particularly if they take the medication on an empty stomach. Taking naltrexone with food can often reduce or eliminate nausea.
Headache
Headaches are relatively common when starting naltrexone. They’re usually mild and temporary. Staying hydrated and giving your body time to adjust can help.
Dizziness
Some people experience mild dizziness or lightheadedness during the first week of treatment. This typically improves as your body adapts to the medication.
Fatigue
It’s not unusual to feel slightly more tired than normal during the adjustment period. For most people, this also resolves within the first couple of weeks.
Sleep Changes
Some people report:
- Vivid dreams
- Restless sleep
- Difficulty falling asleep
Sleep-related side effects tend to improve over time. If they persist, your healthcare provider may recommend adjusting the timing of your dose.
Digestive Changes
Some people experience:
- Stomach discomfort
- Mild cramping
- Diarrhea
- Reduced appetite
These symptoms are usually temporary and often improve within the first few weeks.
How Long Do Naltrexone Side Effects Last?
For most people, side effects are strongest during the first several days and begin improving within one to two weeks.
This adjustment period can be frustrating, especially because naltrexone’s benefits tend to build more gradually. While side effects often show up right away, meaningful changes in cravings, drinking patterns, and alcohol’s pull tend to emerge over weeks and months of consistent use.
That timing mismatch creates a challenge. Some people stop taking naltrexone before they’ve had a chance to experience its full benefits. Studies have found that many patients never refill their initial prescription despite strong evidence supporting the medication. In one study led by Dr. Henry Kranzler, more than half of patients who filled an initial prescription did not continue treatment long term.
Research suggests that people who stay on naltrexone longer often experience larger reductions in cravings, heavy drinking days, and overall alcohol consumption. In other words, one of the biggest challenges with naltrexone isn’t whether it works. It’s staying on it long enough to find out how well it works for you.
That’s one reason programs that combine medication with behavioral support tend to produce stronger outcomes. The same principle guides the Sunnyside Med approach today, combining medication with coaching, accountability, and habit-change tools designed to help people stay engaged through the early adjustment period and beyond.
“Tracking my drinks and starting the medication has been a game changer,” said one Sunnyside Med member. “This is the first time in many years I’m starting to take control.”
Tips for Managing Naltrexone Side Effects
Here are a few methods you can use to navigate naltrexone side effects. Remember, your Sunnyside Med care team is available to answer questions and provide support throughout the process.
1. Take It With Food
Taking naltrexone with a meal or snack is one of the simplest ways to reduce nausea and stomach discomfort.
2. Stay Hydrated
Adequate hydration may help reduce headaches, dizziness, and fatigue.
3. Follow Your Prescribed Timing
If you’re taking naltrexone as part of a moderation program, your provider may recommend taking it one to two hours before your typical drinking window or strongest cravings.
4. Give It Time
Many side effects improve naturally as your body adjusts. If symptoms aren’t debilitating, it may be worth giving yourself a week or two before deciding whether the medication is a good fit.
Serious (But Rare) Side Effects
Serious side effects are uncommon but can occur. You should contact your healthcare provider immediately if you experience any of the following.
Signs of Liver Problems
- Yellowing of the skin or eyes
- Dark urine
- Severe upper-right abdominal pain
- Persistent nausea that worsens over time
Allergic Reactions
- Swelling of the face, lips, tongue, or throat
- Difficulty breathing
- Severe rash
Opioid Withdrawal
Because naltrexone blocks opioid receptors, taking it while opioids are still in your system can trigger sudden withdrawal symptoms.
Significant Mood Changes
Seek medical attention if you experience:
- Severe depression
- Suicidal thoughts
- Dramatic changes in mood or behavior
When Should You Contact Your Care Team?
Reach out to your Sunnyside Med care team or other provider if:
- Side effects persist beyond two weeks
- Side effects interfere with daily life (e.g., they prevent eating or sleeping)
- You’re considering stopping the medication
- The medication is causing symptoms from the “Serious (But Rare) Side Effects” list
How Sunnyside Med Can Help You Manage Naltrexone Side Effects
The challenge for many people isn’t whether naltrexone works. It’s staying on it long enough to experience the benefits. That’s where support becomes especially vital.
At Sunnyside Med, members receive care from licensed medical providers who can help determine whether naltrexone is a good fit, answer questions about side effects, and make adjustments to dosing or titration schedules when appropriate. Starting with a lower dose, changing when you take the medication, or simply knowing what to expect can make the adjustment period much easier.
Members also receive coaching, tracking tools, and a personalized plan designed to help them build sustainable drinking habits while the medication does its work. Research has consistently shown that support can help people stay engaged with treatment and behavior change efforts over time, and Sunnyside’s results back this up: Internal data shows that engaged members are 3x more likely to refill their medication.
The first week on naltrexone isn’t always the easiest. But for many people, a few days of temporary side effects can lead to lasting changes in cravings, drinking patterns, and overall health.
“I’m honestly shocked in the best way by how this medication is making me feel,” said one Sunnyside Med member. “For the first time in a long time, I don’t feel that constant pull to reach for a glass of wine.”
If you’re interested in learning more, check out our complete Naltrexone 101 guide or take a quick assessment to find out whether Sunnyside Med might be a good fit for your goals.
Naltrexone is a prescription medication. This content is educational and should not be taken as medical advice. A licensed clinician reviews every Sunnyside Med application.
Frequently Asked Questions: Naltrexone Side Effects
What is the most common side effect of naltrexone?
Nausea is the most commonly reported side effect, especially during the first few days of treatment. Some people also experience headaches, fatigue, dizziness, or sleep changes as their body adjusts.
The encouraging news is that these side effects are usually mild and temporary.
How long do naltrexone side effects last?
For most people, side effects are strongest during the first several days and improve within one to two weeks. Many of naltrexone’s benefits also build over time, so the first week doesn’t necessarily predict your long-term experience with the medication.
Does everyone experience naltrexone side effects?
No. Some people notice several side effects when they start naltrexone, while others notice almost none. Factors like dose, timing, and whether you take the medication with food can also influence the experience.
Can naltrexone affect sleep?
It can. Some people report vivid dreams, restless sleep, or difficulty falling asleep when they first start taking naltrexone. These effects often improve as the body adjusts.
Can I still drink alcohol while taking naltrexone?
Yes. Unlike Antabuse (disulfiram), naltrexone does not make you sick if you drink alcohol.
Many people use naltrexone specifically to help reduce drinking rather than quit completely. Whether your goal is moderation or abstinence, the medication works by reducing alcohol’s rewarding effects over time.
Should I stop taking naltrexone if I’m experiencing side effects?
Not necessarily. Many side effects improve during the first couple of weeks. Before stopping the medication, talk with your healthcare provider. Small adjustments can often make side effects much more manageable; just be sure to consult with your clinician before making any changes.
Sunnyside is the Perfect Companion for Your Naltrexone Journey
Sunnyside is the #1 mindful drinking app. Since 2020, we’ve been honing our harm-reduction approach and have helped over 400,000 people cut out 22 million drinks from their baseline habits. 96.7% of our members report success in drinking less, and in a third-party study, our approach was demonstrated to reduce weekly drinking by 33% after 12 weeks.
Think of Sunnyside as the front door for anyone who wants to change their relationship with alcohol. If you want to drink less, we can help you get there. If you want to eventually quit, but want to take a gradual approach, we can make that happen.
When you sign up for Sunnyside, you’ll take a quick 3-minute quiz, then hop into the app. It’s as simple and quick as that.
We’ll give you weekly plans to gradually reach your drinking goals, and we’ll provide nudges, coaching, exercises, and advice to help you get there.
We have daily tracking and journaling tools, including the option to chat with a real human coach at any time. And our state-of-the-art analytics help you track your progress over time.
Sunnyside is a full-featured mindful drinking app. Naltrexone will actively help you reduce cravings around alcohol, and Sunnyside will help you understand your triggers and patterns, giving you a healthy system for habit change.
If you choose to stop taking naltrexone, the Sunnyside app remains a tool you can keep using to maintain your healthy habits.
Everyone who signs up for Sunnyside gets a free 15-day trial. After that, the subscription is $8.25/month.
Whether you’re currently taking naltrexone or just doing some research on alcohol moderation, we’d love to have you sign up for our 15-day free trial today.
