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The Complete Guide to Valacyclovir Side Effects

Kristin Hall, FNP

Medically reviewed by Kristin Hall, FNP

Written by Our Editorial Team

Last updated 7/01/2020

Overall, valacyclovir is an extremely safe and well tolerated drug that’s used to treat herpes in people of all ages. However, like all medications, valacyclovir side effects are common, and you should be aware of them before using it.

Valacyclovir, which is widely available as Valtrex, comes in several tablet sizes. Because this medication is used to treat a variety of herpes-related issues (ranging from recurring genital herpes to occasional cold sores), the dosage you may be prescribed can vary.

Our guide to valacyclovir dosage and usage covers the most common valacyclovir doses that are used to treat HPV-1, HPV-2 and other viruses such as VZV.

Below, we’ve provided a full list of the potential valacyclovir side effects you might experience while on the medication. We’ve grouped side effects into categories based on how common they are, starting with the most common adverse effects of valacyclovir treatment before covering rare and extremely rare side effects.

Common Valacyclovir Side Effects

While valacyclovir is an extremely safe medication overall, it does have some side effects that occur in a small minority of users. The most common side effects of valacyclovir, which affect more than one percent of users, are:

  • Headache

  • Diarrhea

  • Nausea

  • Vomiting

These side effects affect a small minority of users (although all occur in more than one percent of people that use valacyclovir), with the majority of people that use valacyclovir reporting little or no side effects at all. If you notice any of these symptoms, it's important to discuss them with your doctor so the they might alter your valacyclovir dosage or prescribe you another comparable medication.

Uncommon Side Effects of Valacyclovir

Between 0.1 percent and one percent of patients prescribed valacyclovir for HSV-1, HSV-2 or another virus report the following side effects:

  • Vertigo

  • Dizziness

  • Confusion

  • Sore throat

  • Rash

  • Renal impairment

  • Constipation

  • Abdominal pain

  • Agitation

  • Edema

  • Weakness

Of these side effects, one of the most serious is renal impairment, which we’ve covered in the “Potential Long Term Side Effects of Valacyclovir” section below.

These side effects are very uncommon, affecting between one and 10 of every 1,000 people prescribed valacyclovir.

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Very Uncommon Side Effects of Valacyclovir

Some side effects also occur in a very small percentage of people that take valacyclovir. The side effects listed below affect less than one in every 1,000 people prescribed valacyclovir for HSV-1, HSV-2 or another viral infection. These side effects include:

  • Seizures

  • Neutropenia

  • Leukopenia

  • Fatigue

  • Anorexia

  • Anaphylaxis

  • Stevens-Johnson syndrome

  • Hepatitis

  • Toxic epidermal necrolysis

  • Psychotic symptoms

Potential Long-Term Side Effects of Valacyclovir

Certain valacyclovir side effects can potentially become more common with long-term usage of the drug.

For example, over the long term, valacyclovir can potentially affect kidney function. This makes it important to speak to your doctor about the potential for long-term valacyclovir side effects if you have a history of kidney issues.

Taken long term, particularly in people with existing kidney issues and/or inadequate hydration, valacyclovir can lead to renal toxicity and kidney failure. It can also lead to inflammation of the liver in certain people, particularly those with existing liver health issues.

Another potential long-term side effect of valacyclovir usage is HUS/TTP, or hemolytic-uremic syndrome and thrombotic thrombocytopenic purpura. These similar disorders can lead to the destruction of red blood cells and a low platelet count, preventing your blood’s ability to clot.

HUS/TTP is a very rare side effect of valacyclovir that’s primarily seen in people with HIV. This makes it important to discuss the potential side effects of valacyclovir with your doctor if you’ve been diagnosed with HIV.

Finally, unfavorable valacyclovir interactions may occur if mixed or used in concert with other antiviral and antiretroviral drugs, particularly those used to treat HIV. If you take medication to control HIV or use PrEP medication to lower your risk of HIV contraction, you should discuss this with your doctor before you consider using valacyclovir.

In Closing

Like all medications, valacyclovir has a variety of side effects, most of which are uncommon and relatively mild. On the whole, it’s a safe and effective medication that’s used by millions of people around the world without any significant issues.

Because valacyclovir is typically used only when outbreaks occur, it’s very unlikely that a typical user will be affected by any of the potential long-term effects of valacyclovir usage.

As always, it’s important to take medication safety seriously and pay close attention to potential side effects before using a new drug. If you have concerns about using valacyclovir, your doctor will be able to provide expert advice and information to help you make an informed decision. And if you're looking for more resources, don't hesitate to check out our Valacyclovir 101 guide.

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.