Valacyclovir Side Effects, Dosages, and Interactions

Commonly marketed under the brand name Valtrex, valacyclovir can help provide relief for patients experiencing symptoms from conditions like chickenpox, shingles, genital herpes, and oral herpes.

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What is Valacyclovir? | Treatment Use | Treat Infections | How Long Does it take to Work? | Proper Dose | Side Effects | Drug Interactions

Many common medical conditions, including the childhood disease chickenpox, are caused by viruses.

Antiviral medication technology has improved dramatically over the past several decades, offering hope and relief from symptoms caused by illness from chickenpox to HIV. 

One popular antiviral medication, valacyclovir, can be used to treat a range of medical conditions caused by viruses, including conditions caused by the herpes simplex family of viruses. 

Commonly marketed under the brand name Valtrex, valacyclovir can help provide relief for patients experiencing symptoms from conditions like chickenpox, shingles, genital herpes, and oral herpes.

What Is Valacyclovir?

Valacyclovir is a generic prescription drug that is commonly sold under the brand name Valtrex.

Available in the form of an oral tablet only, valacyclovir belongs to a class of drugs called nucleoside analogs.

These medications work by mimicking one of the building blocks of DNA in order to stop the replication of viral DNA. Without the ability to replicate, the virus is unable to multiply and spread throughout the body.

Valacyclovir may be used on its own or in combination with other medications.

Although best known for its treatment of genital herpes under the brand name Valtrex, the medication also has a number of other uses and applications in the treatment of certain viruses.

Valacyclovir was first approved by the U.S.Food and Drug Administration (FDA) in 1995 under the brand name Valtrex.

Since the expiration of the original patent in 2009, the medication has been available for sale under its generic name, valacyclovir.

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What Is Valacyclovir Used To Treat?

Valacyclovir is used to treat viral infections caused by herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2), as well as varicella-zoster virus (VZV).

The herpes simplex virus types are responsible for genital and oral herpes while the varicella-zoster virus is responsible for chickenpox and shingles.


Chickenpox, the common childhood illness, occurs as a result of infection with the varicella zoster virus.

The condition causes small red bumps to spread across the body in an itchy rash. At first, the condition may look like insect bites or pimples.

Children with chickenpox are typically very itchy and may experience flu-like symptoms, including tiredness, fever, or body aches.

Valacyclovir can help to reduce the discomfort associated with chickenpox and may be prescribed to children between the ages of 2 and 18 who develop the condition and are not immunocompromised.


Like chickenpox, shingles is caused by the varicella zoster virus.

However, it commonly affects adults.

This condition typically affects individuals who experienced chickenpox as children. Shingles is a serious illness that causes small, painful blisters to appear on the skin.

The blisters may occur throughout the body or just on a small part of the body, and the breakouts are sometimes attributed to stress.

Valacyclovir can be used to reduce discomfort caused by shingles.

Genital Herpes

Genital herpes is a sexually transmitted disease that causes small, painful blisters on or around the genital areas.

Spread through sexual contact, genital herpes is primarily caused by the herpes simplex virus type 2 and can be spread even when a person is not experiencing a flare up of the condition.

Valacyclovir can be used to reduce symptoms caused by a flare up of genital herpes and can also be used to prevent future flare ups in people who are not immunocompromised.

Oral Herpes

Oral herpes, sometimes referred to as cold sores, are small, painful blisters or sores that occur in or around the mouth, typically around the lips.

Oral herpes, also called herpes labialis, is usually caused by the herpes simplex virus type 1.

Oral herpes is spread by kissing or other skin to skin contact with an infected area; however, an individual does not need to be experiencing a flare up in order to spread the virus.

How Does Valacyclovir Treat Viral Infections?

Valacyclovir works in a variety of ways to treat viral infections caused by viruses in the herpes simplex family.

When ingested, the body converts valacyclovir into acyclovir. Once the medication is converted, it begins to inhibit viral DNA replication in two different ways. 

First, it works by inhibiting viral DNA polymerase and preventing the incorporation and termination of the growing viral DNA chain.

Second, it deactivates viral DNA polymerase. As a result, the viral infection is not able to spread, which helps to reduce symptoms and make the patient feel better more quickly. 

Valacyclovir works to suppress an active infection; it does not kill the virus as the virus can remain dormant in the body for years.

How Long Does It Take For Valacyclovir To Work?

The length of time it takes for patients to begin experiencing relief from symptoms depends on the reason why they are taking valacyclovir and the severity of the infection.

Patients experiencing an initial herpes outbreak or mild recurring symptoms will likely start to experience relief within two to three days. 

However, it may take longer to experience relief for severe outbreaks. Valacyclovir works best when it is taken quickly (within 48 hours) after symptoms emerge, so talk to your doctor about a prescription as soon as you notice symptoms.

How Do I Know What Dose of Valacyclovir To Take?

The dose of valacyclovir varies depending on the age of the patient and the reason for treatment. 

When taken for the treatment of chickenpox in children, valacyclovir is typically given as a dose of 20 milligrams (mg) per kilogram (kg) of body weight, and the dose is administered three times per day for five days.

Adults and children under the age of two should not be given valacyclovir for chickenpox unless determined necessary by a doctor.

For the treatment of shingles, adults typically take a dose of 1000 mg three times per day for a period of seven days. Valacyclovir is generally not prescribed to children for shingles, as it more commonly affects older adults, particularly those over the age of 55.

For the treatment of an initial outbreak of genital herpes, adults typically take 1000 mg of valacyclovir twice per day for a total of 10 days.

For the treatment of recurrent outbreaks, adults are typically prescribed a dose of 500 mg of valacyclovir taken twice per day for a total of three days.

For the prevention of genital herpes outbreaks, adults typically take 500 or 1000 mg of valacyclovir once per day.

Children needing to take valacyclovir for genital herpes must receive guidance from their doctor regarding the appropriate dosage and frequency for the medication.

For the treatment of oral herpes, adults typically take 2000 mg twice per day for one day, as do children ages 12 and older.

Children under the age of 12 must have their dose determined by a doctor.

Are There Any Side Effects of Valacyclovir?

Valacyclovir is known to cause some side effects with use.

Side effects associated with valacyclovir include common side effects, which usually do not require medical attention, and serious side effects, which require immediate medical attention. 

Common side effects associated with valacyclovir include:

  • Headache
  • Vomiting
  • Pain in the abdomen or stomach area
  • Nausea
  • Dizziness

Serious side effects of valacyclovir require immediate medical attention. These side effects include:

  • Kidney failure, as evidenced by:
    • Urinating less often than normal
    • Severe drowsiness
    • Swelling of the feet, ankles, or legs
  • Central nervous system effects, including:
    • Shaky or unsteady movements
    • Hallucinations
    • Aggressive behavior
    • Confusion
    • Seizures
    • Coma

What Drug Interactions Are Associated With Valacyclovir?

Some medications may interact with valacyclovir. Certain medications may increase a patient’s risk of experiencing side effects, decrease the effectiveness of one or both medications, or affect the length of time that one or both medications work.

Some medications that are known to interact with valacyclovir include:

  • Cimetidine
  • Clozapine
  • Varicella virus vaccination
  • Zoster virus vaccination
  • Antiviral medications
  • Tenofovir
  • Warfarin
  • Clopidogrel
  • Hepatitis B medications
  • Non-steroidal anti-inflammatory drugs (NSAIDs)
  • Probenecid
  • Theophylline
  • Zidovudine


Valacyclovir is an antiviral medication that is commonly used for the treatment of chickenpox, shingles, genital herpes, and oral herpes. 

The most common side effects of valacyclovir include headache, nausea, vomiting, abdominal pain, and dizziness.

Rarely, valacyclovir can cause kidney failure or central nervous system effects. 

The medication comes in the form of an oral tablet that is taken anywhere from one to three times per day. In addition to treating outbreaks of chickenpox, shingles, genital herpes, and oral herpes, valacyclovir can also be used to prevent outbreaks of genital herpes in patients who experience recurring outbreaks.

References, Studies and Sources: 

We are committed to providing our readers with only trusted resources and science-based studies with regards to medication and health information. 

Disclaimer: This general information is not intended to diagnose any medical condition or to replace your healthcare professional. If you suspect medical problems or need medical help or advice, please talk with your healthcare professional.

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