Valtrex (Valacyclovir) – Oral

What Is Valtrex?

Valtrex (valacyclovir) is a medication prescribed to treat certain viral infections, including chicken pox, cold sores, and other conditions caused by herpes viruses.

Valtrex is part of a class of antiviral drugs called nucleoside analogs. It prevents the viral growth of herpes by interfering with gene replication, the process in which a DNA molecule makes two copies of itself during cell division. This medication comes as a tablet that is taken by mouth.

Drug Facts

Generic Name: Valacyclovir

Brand Name(s): Valtrex

Drug Availability: Prescription

Therapeutic Classification: Antiviral

Available Generically: Yes

Controlled Substance: N/A

Administration Route: Oral

Active Ingredient: Valacyclovir

Dosage Form(s): Tablet

What is Valtrex Used For?

The Food and Drug Administration (FDA) approved Valtrex for the following indications:

  1. For ages 2 to 18: Chicken pox, a contagious infection caused by herpes varicella zoster virus
  2. For ages 12 and older: Cold sores, usually caused by herpes simplex virus 1 (HSV-1)
  3. For ages 18 and older:
  • Genital herpes, usually caused by herpes simplex virus 2 (HSV-2)  
  • Prevention of transmission of HSV
  • Suppression of HSV
  • Suppression of HSV for people who are immunosuppressed due to human immunodeficiency virus (HIV)
  • Shingles, which is caused by reactivation of varicella zoster and produces a painful rash

The dosing of Valtrex differs for children and adults and is based on weight for the treatment of chicken pox. Valtrex is used short term for the treatment of chicken pox, shingles, and cold sores.

It can also be used for the short-term treatment of genital herpes or long term to suppress the virus and prevent transmission to a partner. However, it is important to remember that Valtrex will not cure your herpes infection completely.

Valtrex (Valacyclovir) Drug Information - Illustration by Dennis Madamba

Verywell / Dennis Madamba

How to Take Valtrex

Valtrex is a tablet that should be swallowed. You can take Valtrex with or without food. It is important to stay hydrated when using Valtrex.

If you are taking Valtrex for cold sores, chicken pox, shingles, or genital herpes, start treatment as soon as possible after your symptoms start. Initial signs of infection may include tingling, itching, or burning, or when the sore appears.

Storage

Store Valtrex tablets at a temperature of 59–77 degrees Fahrenheit. Keep the medication in its original container and away from children or pets.

Off-Label Uses

Valtrex has been used for the treatment of other antiviral conditions besides the approved indications, also known as “off-label” use.

Valtrex is sometimes prescribed for the off-label treatment of:

  • Cytomegalovirus (CMV): This viral infection can be transmitted from a pregnant mother to a baby, potentially causing brain and/or liver damage to the baby. Valtrex has been prescribed for people who have CMV infection during pregnancy to reduce transmission to the baby.
  • Bell’s palsy: This condition is characterized by temporary paralysis of one side of the face. It is believed to be associated with a reaction to a viral infection. Valtrex can sometimes be effective in treating Bell’s palsy.

How Long Does Valtrex Take to Work?

Valtrex should start to have an effect on the body within a few hours of taking it. However, it may take several days of treatment before you start noticing your symptoms getting better.

What Are the Side Effects of Valtrex?

This is not a complete list of side effects, and others may occur. A medical professional can advise you on side effects. If you experience other effects, contact your pharmacist or a medical professional. You may report side effects to the FDA at www.fda.gov/medwatch or 800-FDA-1088.

Valtrex can cause several side effects, most of which are not dangerous. However, some serious side effects can occur.

Common Side Effects

Common side effects of Valtrex include:

Headaches are the most common side effect that children experience when taking Valtrex. Be sure to discuss any side effects that you have with your healthcare provider and let them know if your symptoms worsen.

Severe Side Effects

Severe side effects caused by Valtrex can affect anyone. However, severe side effects are more common in older adults, people who take nonsteroidal anti-inflammatory medications (NSAIDs), including aspirin, Advil or Motrin (ibuprofen), and Aleve (naproxen sodium), and people who have kidney disease.

Some severe side effects associated with Valtrex include:

  • Thrombotic thrombocytopenic purpura (TTP): This condition causes blood clots in the small blood vessels throughout the body, often with bruising. 
  • Hemolytic uremic syndrome (HUS): This condition causes blood clots and bleeding throughout the body. 
  • Acute kidney failure: Severe damage can cause the kidneys to rapidly stop functioning. Symptoms include dizziness, confusion, dark urine, a reduced amount of urine, or a complete lack of urine. This condition generally resolves with treatment
  • Neurotoxicity: Nervous system effects can include agitation, hallucinations, confusion, delirium, seizures, and encephalopathy. These symptoms are expected to get better after Valtrex is stopped.

If you develop any signs of these problems, seek prompt medical attention.

Long-Term Side Effects

The effects of TTP and HUS can be fatal or may cause lasting organ damage.

Report Side Effects

Valtrex may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much Valtrex Should I Take?

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The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For oral dosage form (tablets):
    • For treatment of chickenpox:
      • Adults and children below 2 years of age—Use and dose must be determined by your doctor.
      • Children 2 to 18 years of age—Dose is based on body weight and must be determined by your doctor. The usual dose is 20 milligrams (mg) per kilogram (kg) of body weight, taken three times a day for 5 days. However, the dose is usually not more than 1000 mg three times a day.
    • For treatment of cold sores:
      • Adults—2000 milligrams (mg) every 12 hours for one day.
      • Children 12 years of age and above—2000 milligrams (mg) every 12 hours for one day.
      • Children below 12 years of age—Use and dose must be determined by your doctor.
    • For treatment of genital herpes, first outbreak:
      • Adults—1000 milligrams (mg) two times a day for ten days.
      • Children—Use and dose must be determined by your doctor.
    • For treatment of genital herpes, recurrent outbreaks:
      • Adults—500 milligrams (mg) two times a day for three days.
      • Children—Use and dose must be determined by your doctor.
    • To prevent recurrent outbreaks of genital herpes:
      • Adults—500 milligrams (mg) or 1000 mg once a day.
      • Children—Use and dose must be determined by your doctor.
    • For treatment of shingles:
      • Adults—1000 milligrams (mg) three times a day for seven days.
      • Children—Use and dose must be determined by your doctor.

Modifications

Having certain medical conditions may increase your risk of side effects or require that you take a lower dose.

Let your healthcare provider know if you:

  • Have had a bone marrow transplant or kidney transplant
  • Have advanced HIV disease, or AIDS
  • Have kidney problems

Also, if you are aged 65 years or older you may need a lower dose of Valtrex.

For children who cannot swallow pills, your healthcare provider can prescribe Valtrex as an oral suspension. 

Talk to your provider if you become pregnant, are planning to become pregnant, or are breastfeeding. They will help determine the risks and benefits of taking this medication.

Missed Dose

Ask your healthcare provider how to proceed if you miss a dose of Valtrex. Generally, you can take your dose as soon as you remember that you missed it. Take your next dose at its regular time. However, do not take the missed dose if it is almost time for your next scheduled dose.

Overdose: What Happens If I Take Too Much Valtrex?

If you take too much Valtrex, it can lead to acute kidney damage. This is a medical emergency that can cause toxicity in your body and the inability to make urine.

Hemodialysis is a procedure that helps your body eliminate toxins and balance fluid—this may be necessary until your kidney function is restored.

What Happens If I Overdose on Valtrex?

If you think you or someone else may have overdosed on Valtrex, call your healthcare provider or the Poison Control Center (800-222-1222). 

If someone collapses or isn’t breathing after taking Valtrex, call 911.

Precautions

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If you or your child's symptoms do not improve within a few days, or if they become worse, check with your doctor.

The areas affected by genital herpes, chickenpox, or shingles should be kept as clean and dry as possible. Also, wear loose-fitting clothing to avoid irritating the sores (blisters).

It is important to remember that this medicine will not keep you from spreading herpes to others.

Herpes infection of the genitals can be caught from or spread to your partner during any sexual activity. Even though you may get herpes if your partner has no symptoms, the infection is more likely to be spread if sores are present. This is true until the sores are completely healed and the scabs have fallen off. Therefore, it is best to avoid any sexual activity if either you or your sexual partner has any symptoms of herpes. The use of a latex condom (“rubber") may help prevent the spread of herpes. However, spermicidal (sperm-killing) jelly or a diaphragm will probably not help.

What Are Reasons I Shouldn’t Take Valtrex?

You should not take Valtrex if you are allergic to any of its ingredients or the antiviral medication acyclovir.

What Other Medications May Interact With Valtrex?

There are no clinically significant drug interactions with Valtrex.

What Medications Are Similar?

There are several antiviral medications that are similar to Valtrex but do not have identical approved indications. These include:

  • Sitavig and Zovirax (acyclovir): This medication is available as a tablet or a liquid to be swallowed. It is also available in an injectable form to be used for severe HSV infections, including HSV encephalitis (brain infection). It is also available as a cream for the treatment of cold sores. 
  • Famvir (famciclovir): This is available as a tablet for the treatment of cold sores, genital herpes, and shingles. 

Many other antiviral medications are used for treating different infections. For example, Epivir (lamivudine) and Viread (tenofovir) are used to treat HIV. Baraclude (entecavir) is used to treat hepatitis B.

Frequently Asked Questions

  • What is Valtrex used for?

    Valtrex is used to treat cold sores, genital herpes, chicken pox, and shingles. These infections are caused by herpes viruses.

  • How does Valtrex work?

    Once it is in the body, Valtrex converts to acyclovir, which actively fights against the virus. Valtrex treats viral infections by inhibiting the multiplication of herpes simplex virus (the virus that causes cold sores and genital herpes) and varicella zoster virus (the virus that causes chicken pox and shingles).

  • What drugs should not be taken with Valtrex?

    You should not take Valtrex with other drugs that have the potential to harm the kidneys if you have a kidney problem.

  • How long does it take for Valtrex to work?

    Valtrex is absorbed quickly and should start having an effect on the body within a few hours. It is recommended to take this medication as soon as symptoms begin. You might not notice clinical improvement of symptoms until you have been taking Valtrex for several days.

  • What are the side effects of Valtrex?

    The most common side effects are headaches, nausea, and abdominal pain. Serious side effects are rare and include kidney failure, behavioral changes, seizures. Thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) are rare, severe blood clotting and bleeding conditions that can occur due to taking Valtrex.

  • How to stop taking Valtrex?

    You can stop taking Valtrex when your prescribed dose is complete. You might have a follow-up visit with your healthcare provider to assess whether your infection has resolved.

How Can I Stay Healthy While Taking Valtrex?

There are several considerations that you must keep in mind to stay healthy while you are taking Valtrex: 

  • Maintain hydration: Valtrex is more likely to cause kidney damage if you are dehydrated. 
  • Pain control for shingles: Shingles can cause substantial pain. Your healthcare provider may prescribe a pain-control medication for you as your condition is resolving.
  • Rest and fever control for chicken pox: Chicken pox infection can cause high fevers and sometimes fatigue. If your child has this infection, maintain rest, and follow their provider’s advice regarding management of fevers.

Herpes viruses are highly contagious, so it’s important to avoid infecting others while you are recovering.

Tips to avoid the spread of the following infections:

  • Cold sores: Don’t share cups, utensils, lipstick, or kiss others while a cold sore is present 
  • Genital herpes: Practice safe sex. 
  • Chicken pox and shingles: Avoid contact with people who are immunosuppressed (such as due to cancer treatment or HIV), people who are pregnant, and babies until your infection has fully resolved. 

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended as a replacement for medical advice, diagnosis, or treatment from a healthcare professional. Consult your doctor before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

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  1. Kausar S, Said Khan F, Ishaq Mujeeb Ur Rehman M, et al. A review: Mechanism of action of antiviral drugs. Int J Immunopathol Pharmacol. 2021 Jan-Dec;35:20587384211002621. doi:10.1177/20587384211002621

  2. Food and Drug Administration. Valtrex label.

  3. De Santis M, Apicella M, De Luca C, et al. Valacyclovir in primary maternal CMV infection for prevention of vertical transmission: A case-series. J Clin Virol. 2020 Jun;127:104351. doi:10.1016/j.jcv.2020.104351

  4. Cao J, Zhang X, Wang Z. Effectiveness comparisons of antiviral treatments for Bell palsy: a systematic review and network meta-analysis. J Neurol. 2021 Mar 5. doi:10.1007/s00415-021-10487-9

  5. Azmaiparashvili Z, Lo KB, Habib N, Hsieh A. When a seemingly harmless prescription turns into toxicity. Case Rep Med. 2018 Sep 16;2018:9724390. doi:10.1155/2018/9724390

  6. Inaba I, Kondo Y, Iwasaki S, et al. Risk evaluation for acute kidney injury induced by the concomitant use of valacyclovir, analgesics, and renin-angiotensin system inhibitors: The detection of signals of drug-drug interactions. Front Pharmacol. 2019 Aug 8;10:874. doi:10.3389/fphar.2019.00874