What are naltrexone side effects?

Alcohol Use Disorder

The most common are nausea, headache, and trouble sleeping, usually mild and gone within a week or two. Serious ones are rare.

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Side effects at a glance

What most people notice, and the rare serious signs

Most common

Nausea, headache, sleep

Also possible

Anxiety, aches, low appetite

Shot site (Vivitrol)

Soreness or a small lump

Rare but serious

Liver, allergy, mood

When they start

First few days

Most fade within

1 to 2 weeks

Causes weight gain?

No

Need treatment?

Usually not

Most people take it with little trouble once the first few days pass.

1 to 2

weeks for most side effects to fade as your body adjusts

25 mg

a gentle starting dose many providers use for a few days before the full 50 mg

Rare

serious side effects are uncommon, and most need no treatment at all

The most common side effects of naltrexone are nausea, headache, dizziness, tiredness, and trouble sleeping. They are usually mild and tend to fade within the first week or two. Serious side effects are rare, and most people take naltrexone with little trouble once they get past the first few days.

Common naltrexone side effects

The side effects most people notice are mild and happen early. Nausea is the most common, especially in the first few days, and it usually settles quickly. Other common effects include headache, dizziness, feeling tired, trouble sleeping, and some stomach upset. Some people also feel a little anxious or notice aches, a lower appetite, or vivid dreams. For the great majority of people, these fade within one to two weeks as the body adjusts.

Most side effects fade within one to two weeks.They tend to be mild, they usually need no treatment, and they often ease on their own as your body gets used to the medication.

How to manage the early side effects

A few simple steps make the first weeks easier. Taking your pill with food helps calm nausea. Many providers start you at 25 mg for a few days, then move up to the full 50 mg, so your body eases into it. Staying hydrated and taking the dose at a consistent time each day help too. If trouble sleeping is a problem, ask your provider about the best time of day to take it. Most side effects do not need any treatment and simply go away on their own.

Injection-specific side effects (Vivitrol)

The monthly Vivitrol injection can cause the same effects as the pill, plus a reaction at the injection site. That usually means soreness, redness, swelling, or a small lump where the shot was given, and it typically clears on its own. Rarely, the injection site can develop a more serious reaction with significant pain, hardening, or tissue damage. Tell your provider if injection-site pain is severe or does not improve, since it may need attention.

Rare but serious side effects

Serious side effects are uncommon, but it helps to know the signs. At very high doses, naltrexone can irritate the liver, so watch for stomach pain that does not go away, dark urine, or yellowing of the skin or eyes. Allergic reactions are rare but can cause rash, swelling, or trouble breathing. Some people may notice mood changes or low mood, so tell your provider if you feel unusually down. And because naltrexone blocks opioids, starting it too soon after opioids can cause sudden withdrawal.

Call your provider or seek care if you notice: ongoing stomach pain, dark urine, or yellow skin or eyes (possible liver signs); a severe or worsening injection-site reaction; rash, swelling, or trouble breathing (possible allergy); or new or worsening depression. Also remember that after you stop naltrexone, your tolerance to opioids is lower, which raises overdose risk if you return to them.

Common vs. serious side effects

Here is a quick side-by-side of the everyday effects most people feel and the rare ones that mean you should call a provider.

For related reading, see our naltrexone for alcohol guide, what to avoid on naltrexone, drug interactions, and dosage guide.

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