Key takeaways

  • Valacyclovir oral tablet is a generic prescription medication for viral infections like herpes simplex, shingles, and chickenpox. It can cause side effects ranging from mild to serious, including long-term effects like kidney problems or changes in thinking or behavior.
  • More common mild side effects of valacyclovir oral tablet include headache and nausea. These can often be managed with over-the-counter pain relievers or by taking the medication with food.
  • While generally considered safe to use during pregnancy, valacyclovir should be discussed with a doctor if you are pregnant or breastfeeding.
  • Certain pre-existing conditions like kidney problems or HIV/AIDS can increase the risk of serious side effects from valacyclovir.

Valacyclovir is a generic prescription drug used to treat the following conditions:

It comes as tablet that you swallow. The brand-name version of valacyclovir oral tablet is called Valtrex.

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Valacyclovir’s more commonly reported side effects include:

For more information about some of these side effects, see the “Managing side effects” section.

Examples of mild side effects that have been reported with this drug include:

  • abdominal pain
  • vomiting
  • dizziness
  • headache
  • nausea

For more information about some of these side effects, see the “Managing side effects” section.

These side effects are usually temporary. And some may be easily managed. But if you have any symptoms that are ongoing or bother you, talk with your doctor or pharmacist. And do not stop taking valacyclovir unless your doctor recommends it.

For more information about some of these side effects, see the “Managing side effects” section.

Valacyclovir may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

Serious side effects of valacyclovir include:

For more information about some of these side effects, see the “Managing side effects” section.

The list above does not include all possible serious side effects of valacyclovir. For more information, see valacyclovir’s prescribing information.

If you develop serious side effects while taking valacyclovir, call a doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Sharing your experience helps make medication safer for everyone by giving doctors and researchers more information about how the drug works in real life. If you develop a side effect while taking valacyclovir and want to tell the FDA about it, visit MedWatch or call 800-FDA-1088.

Allergic reaction

For some people, valacyclovir can cause an allergic reaction. While this side effect wasn’t reported in studies of valacyclovir, it has been reported since the drug came on the market.

In general, symptoms of an allergic reaction can be mild or serious.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should keep taking valacyclovir.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to valacyclovir, they may have you switch to a different treatment.

Children taking valacyclovir experienced many of the same side effects reported in adults taking the drug. But children also experienced:

If your child or a child you care for is taking valacyclovir and you have questions or concerns about side effects of the drug, talk with a doctor or pharmacist.

Here are more details about some of the side effects valacyclovir may cause and how to manage them.

Kidney problems

Although rare, it’s possible for valacyclovir to cause kidney problems. Specifically, this drug may increase the risk of acute kidney failure in:

What might help

Your doctor may recommend monitoring you for symptoms of kidney problems throughout your treatment with valacyclovir. Symptoms may include:

You should drink plenty of water while taking valacyclovir to help prevent dehydration. Staying hydrated may reduce your risk of developing acute kidney failure as a side effect.

If you develop symptoms of kidney problems, your doctor will likely have you stop taking valacyclovir. They can recommend the best treatment for your kidney problems as well as the condition you’re taking valacyclovir to treat.

Headache

It’s possible for valacyclovir to cause headache. This was one of the most common side effects reported by those taking the drug.

What might help

Talk with your doctor if you experience headaches from valacyclovir. If they’re severe or bothersome, your doctor may be able to recommend ways to decrease this side effect. For example, they may recommend taking an over-the-counter pain medication, such as ibuprofen (Advil) or acetaminophen (Tylenol).

Nausea

You may experience nausea from taking valacyclovir. This was one of the most common side effects reported by people taking the drug.

What might help

If you feel nauseous during your valacyclovir treatment, talk with a doctor or pharmacist. They may be able to recommend ways to decrease this side effect. For example, taking medications with food can sometimes help.

Here are answers to some frequently asked questions about valacyclovir’s side effects.

Yes, valacyclovir can cause long-term side effects, though these were not common in the drug’s studies. For example, valacyclovir may cause kidney problems or changes to your thinking or behavior, such as confusion or hallucinations. These side effects may continue even if you stop treatment with the drug.

If you have questions or concerns about valacyclovir’s long-term side effects, talk with a doctor or pharmacist.

It’s possible you could experience hair loss from taking valacyclovir, though this wasn’t a side effect reported in studies of the drug. It’s been reported as a possible side effect since the Food and Drug Administration (FDA) approved the drug. But it’s not known for sure if valacyclovir caused the hair loss.

If you notice hair loss during valacyclovir treatment, talk with a doctor or pharmacist. They can help determine the cause and the best way to treat it.

It’s possible for valacyclovir to affect your liver, though this wasn’t reported in studies of the drug.

Liver problems, including increased liver function tests and hepatitis, were reported after valacyclovir was approved by the FDA. But it’s not known for sure if valacyclovir was the cause.

It’s important to be aware of symptoms of liver problems, so you can tell your doctor right away if you experience any. Symptoms may include:

If you experience liver problems while taking valacyclovir, your doctor can help to determine the cause and treat the condition.

Before taking valacyclovir, discuss your health history with your doctor. Valacyclovir may not be right for you if you have certain medical conditions or other factors affecting your health.

Be sure to talk with your doctor if any of the following apply to you:

Alcohol and valacyclovir

There aren’t any known interactions between valacyclovir and alcohol. But it’s possible for alcohol to worsen valacyclovir’s side effects. For example, both alcohol and valacyclovir can cause:

  • nausea
  • vomiting
  • headache
  • dizziness

So drinking alcohol while taking valacyclovir may increase your risk of these side effects. Talk with your doctor about how much alcohol, if any, is safe for you to drink while taking this drug.

Pregnancy and breastfeeding while taking valacyclovir

It may be safe to take valacyclovir during pregnancy. Studies of pregnant women taking the drug have not shown an increased risk of problems with fetal development (commonly known as birth defects). But there’s not enough information to determine if the drug may increase the risk of miscarriage.

It’s important to note that untreated herpes simplex virus infections may cause problems to a developing fetus, such as growth problems or stillbirth.

It’s not known if valacyclovir shows up in breast milk. But valacyclovir breaks down into a drug called acyclovir that does show up in breast milk. So it’s likely that a baby who is breastfeeding will be exposed to the drug. At this time, it’s unknown what effects this drug may have on a breastfeeding baby.

If you’re pregnant, planning to become pregnant, or breastfeeding, talk with your doctor before starting valacyclovir treatment.

Side effects of valacyclovir are usually mild. But it’s also possible to experience serious side effects from this drug. If you have questions about side effects the drug can cause, talk with your doctor.

Questions to ask your doctor

  • Is my risk of side effects from valacyclovir higher due to my other medical conditions?
  • How do side effects of valacyclovir compare with other drugs used to treat herpes simplex virus?
  • Does my risk of side effects from valacyclovir depend on my dosage?
  • If I experience side effects, can my dose of valacyclovir be decreased?

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Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.