Naltrexone Nausea and Side Effects Guide

The short answer

Nausea is one of the side effects people most often ask about with naltrexone. In research, nausea was more common with naltrexone than placebo. When it happens, it is often early, mild, and temporary, but any side effect should be discussed with your clinician.

Side effects are a reasonable thing to ask about. If you are considering a medication to help you drink less, you should know what people commonly notice, what usually passes, and what deserves a message to your clinician.

The side effect people ask about most: nausea

Nausea is one of the better-known naltrexone side effects. A 2023 JAMA systematic review found that nausea was more common with naltrexone than placebo. Clinical trial data cited by GoodRx puts the figure more concretely: nausea and vomiting affect up to 10% of people taking naltrexone for alcohol use disorder, and headache affects roughly 7%. That does not mean everyone gets it. It means it is common enough to discuss upfront, yet uncommon enough that the majority of people do not experience it at all.

For context, these figures come from trials where participants were monitored closely and asked to report any discomfort, which tends to surface mild symptoms that might otherwise go unmentioned. In everyday clinical practice, many people start the medication and notice nothing remarkable in the first week.

It is also worth putting the 10% figure in perspective. In the same trials, the placebo group also reported nausea, just less frequently. That gap represents the medication's contribution, but it also shows that the human body is already pretty good at generating stomach discomfort on its own, especially when drinking patterns are shifting. Some of what people attribute to the pill may partly be the body noticing the change in alcohol intake.

When nausea happens, it often shows up in the first few days as the body adjusts to the medication. Many people who notice it describe it as mild and short-lived: an unpleasant week, not a reason the medication cannot work for them. Taking naltrexone with food, and not on an empty stomach, is one simple strategy that can reduce stomach discomfort. Some people find that taking it at night, and not in the morning, means any stomach upset happens during sleep and not during the day. Some people feel noticeably better after the first week or two, once the adjustment period passes.

Headache follows a similar pattern. When it appears, it tends to be early and temporary. It is worth noting that both nausea and headache can also be associated with the process of cutting back on alcohol itself, the body noticing a change, which makes it genuinely difficult to tell cause from effect without some guidance. A clinician can help you work out whether what you are feeling is the medication, the shift in drinking, or the normal noise of a body recalibrating. That distinction matters, and it is one reason having a clinician involved from the start is a real part of the process, not a box to tick.

Sleep changes are another effect that catches some people off guard. A subset of people report vivid dreams or slightly disrupted sleep in the first one to two weeks, particularly if they were relying on alcohol to fall asleep. As drinking decreases, sleep architecture genuinely changes, sometimes uncomfortably at first. Alcohol suppresses REM sleep, so when alcohol is reduced, the brain essentially rebounds into deeper dreaming. Most people find this normalises within a couple of weeks. If it does not, that is exactly the kind of thing to raise with your clinician, not something to quietly endure.

Common naltrexone side effects at a glance

The following side effects are documented in the DailyMed prescribing label and the 2023 JAMA systematic review. Most are early-onset and resolve within the first one to two weeks as your body adjusts.

Not everyone experiences any of these. The majority of people in clinical trials did not report them. Data sourced from the DailyMed naltrexone label and the JAMA 2023 systematic review.

What Onir members are reporting

Onir's current member-reported data shows that fewer than 20% of members report any type of side effect. Among the members who do report side effects, the pattern is generally mild to manageable, and symptoms typically subside within the first two weeks as the body adjusts. Among members who do flag a side effect early, the most common response from their clinician is a simple timing or dosing adjustment, not a recommendation to stop. Taking it at a consistent time each evening is another approach that works well for people who find that any stomach sensitivity overlaps with sleep and not their waking hours.

That does not mean side effects should be ignored. It means the most common experience is either no side effects or short-lived discomfort that can be reviewed with a clinician if needed. Members who flag a symptom early get a response from their clinician: a reassurance, a dosing tweak, or a recommendation to stop, instead of sitting with uncertainty alone. That back-and-forth is part of what makes a clinician-guided approach different from looking up answers online.

Why early side effects do not always mean the medication is wrong for you

The first days of any medication can be the period when your body is adjusting. That is why clinician guidance matters. A side effect may be something to monitor, something to manage, or in some cases a reason to change course. Only someone who knows your history and current medications is well-placed to tell you which one applies.

Some people stop a medication too soon because an early side effect feels alarming, when it would have resolved in a few more days. Others push through something they should have flagged. Neither is ideal. The right answer is not to ignore symptoms. It is to have a clinician involved so you are not making the call alone, and so the decision to continue, adjust, or stop is based on real information and not anxiety or guesswork.

Dosing approach can also matter here. Your clinician may recommend starting at a lower dose for the first few days to let the body ease in before stepping up to the full dose. This is not a universal protocol, but it is one practical tool they might use if you are particularly concerned about early stomach discomfort. Timing is another lever: when to take naltrexone, morning or evening, means the difference between any nausea window overlapping with sleep and not your workday, which many people find far easier to tolerate. It is a conversation worth having during your initial review, before you have already started feeling unwell.

Other side effects people may ask about

People can report different early effects, including headache, tiredness, appetite changes, sleep changes, or stomach discomfort. Not everyone experiences these, and not every symptom is caused by medication. Changes in drinking itself can also change sleep, appetite, and energy.

This is why Onir's process starts with a clinical review and keeps the medication decision individualized.

How to think about side effects in context

For many people, the current drinking pattern already has side effects: worse sleep, lower energy, bigger restaurant bills, missed workouts, next-day anxiety, or weight changes. The question is not medication in a vacuum. The question is whether a clinician-guided plan can help you move toward a better overall tradeoff.

If nausea shows up briefly while drinking starts to come down, many people find that tradeoff manageable. But it still needs to be handled with real medical guidance.

When to contact your clinician

Contact your clinician if side effects feel severe, persistent, unusual, or concerning, or if you have a medical condition, take other medications, or are unsure whether what you are feeling is expected.

Do not use naltrexone if you are currently taking opioids or have used them recently. Starting too soon can trigger sudden, severe withdrawal symptoms, which is why naltrexone treatment typically requires being opioid-free for a period specified by your clinician before the first dose. This is not a technicality; it is a genuine medical risk. Clinicians also screen for other conditions before approving treatment, including liver disease, kidney disease, and pregnancy or breastfeeding. Each of these can affect whether naltrexone is appropriate or require closer monitoring. The upfront assessment exists precisely to handle this screening, so that by the time you start, a real clinician has reviewed your history and confirmed it is safe to proceed.

The positive takeaway

Nausea is worth knowing about, but it should not automatically scare someone away from learning whether naltrexone is appropriate. For many people who experience it, it is mild and temporary. The bigger question is whether the medication helps reduce the pull enough to make drinking less feel possible.

Onir gives you a private way to have that question reviewed by a licensed clinician before you move forward.

FAQ

What is naltrexone and how does it help with drinking less?

Naltrexone is a prescription medication that has been FDA-approved for treating alcohol use disorder for over 30 years. It is non-addictive and non-habit-forming. When you drink, your brain releases a wave of endorphins that reinforces the behavior, which is part of why drinking can feel automatic. Naltrexone gently blocks the receptors that carry that reinforcement, so alcohol feels less rewarding and the pull to keep drinking weakens. Most Onir members notice that pull easing within 10 to 14 days. It works whether your goal is drinking less on weeknights, taking a longer break, or stopping completely. Onir prescribes FDA-approved generic naltrexone hydrochloride 50 mg tablets after a licensed clinician reviews your history.

How long do naltrexone side effects last?

For most people, side effects like nausea, headache, and fatigue are at their most noticeable in the first one to two weeks as the body adjusts. After that initial period, the majority of people find they fade on their own. If a side effect feels severe or is not improving after two weeks, that is worth mentioning to your clinician — it may indicate a need to adjust timing, dosage, or approach.

Does naltrexone cause weight gain or loss?

Naltrexone is not a weight-loss medication, but reduced appetite is listed as a common early side effect in the DailyMed prescribing label. In practice, some people do notice modest weight changes — often because drinking less alcohol means consuming fewer liquid calories. Any significant or unexpected change in weight is worth discussing with your clinician.

What happens if I take naltrexone with opioids in my system?

Taking naltrexone when opioids are in your system can trigger sudden, severe opioid withdrawal — this is one of the most important contraindications. This is not a theoretical concern; it is a genuine medical risk that is one of the primary reasons a clinical review is required before starting. You should be opioid-free for a clinician-specified period before beginning naltrexone, and you should always discuss any pain medications or recent opioid use during your assessment.

Will nausea go away on its own?

For most people, yes. Nausea is most common in the first few days and typically fades within one to two weeks as the body adjusts to the medication. Taking naltrexone with food or at night rather than in the morning can help reduce stomach discomfort in the meantime. If nausea is persistent, uncomfortable, or accompanied by vomiting, contact your clinician — there are practical steps they can take.

Is naltrexone safe for my liver?

At the standard doses used to treat alcohol use disorder (50 mg), naltrexone has not been shown to cause liver damage in people with normal liver function. The DailyMed prescribing label does note that very high doses — well above the therapeutic range — have been associated with liver toxicity in some studies. People with existing liver conditions should discuss this with a clinician before starting, which is part of why an upfront clinical review exists.

Can naltrexone be taken with antidepressants or other medications?

Naltrexone does not have a major interaction with most antidepressants, but it is always important to share your full medication list during your clinical review. Your clinician can flag any combinations worth monitoring before you start.

Does naltrexone cause depression or low mood?

Some people notice a temporary flat or low mood in the early weeks, which can be hard to separate from the emotional shifts that come with changing a drinking habit. If low mood feels persistent or significant, it is worth raising with your clinician rather than assuming it will pass on its own. If you have thoughts of harming yourself, call or text 988 (the Suicide and Crisis Lifeline) right away.

How long do naltrexone side effects last in the first week?

Most side effects like nausea, headache, and fatigue are mild and fade by the end of week one or two. Taking your dose with food helps with stomach-related symptoms. If nausea lingers past two weeks, your clinician can adjust timing or temporarily lower your dose to 25 mg.

What are the naltrexone side effects in the first week, and how long do they last?

The most common side effects are nausea, stomach discomfort, and reduced appetite, and they tend to peak in the first few days then ease by the end of week two. Taking the tablet with food is the simplest way to reduce nausea. Naltrexone does not cause physical withdrawal when you stop, so you can discontinue without tapering if side effects become difficult.

References

1. DailyMed: Naltrexone Hydrochloride label
2. JAMA 2023 systematic review/meta-analysis, PMID 37934220
3. NIAAA: Treatment for Alcohol Problems

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