Generic name: valacyclovir [ val-a-SYE-kloe-veer ]
Brand name: Valtrex
Drug class: Purine nucleosides

What is the drug valacyclovir?

Valacyclovir is a drug used to fight viruses. It makes the herpes virus grow and spread more slowly, which helps the body fight the infection.

Valacyclovir is used to treat infections in adults that are caused by herpes viruses, such as genital herpes, cold sores, and shingles.

Valacyclovir is used to treat cold sores in children over the age of 12 or chickenpox in children over the age of 2.

Valacyclovir won’t get rid of herpes and won’t stop you from giving it to other people. But this medicine can make the signs of an infection less bad.


Tell your doctor if you have HIV/AIDS, a weak immune system, kidney disease (or are on dialysis), or if you have had a kidney or bone marrow transplant before taking valacyclovir.

Valacyclovir can be bad for the kidneys, and this is made worse when it is taken with other drugs that are also bad for the kidneys. Tell your doctor about any other medicines you are taking. When you take certain drugs with valacyclovir, you may need to change the dose or get special tests.

As soon as possible after the first sign of a virus, valacyclovir treatment should begin (such as tingling, burning, blisters).

Genital herpes will still spread even if you take valacyclovir. Herpes infections are contagious, and you can give them to other people even if you are taking this medicine.

Stop taking valacyclovir and call your doctor right away if you have any serious side effects that could hurt your red blood cells, such as fever, easy bruising or bleeding, red spots on your skin that aren’t caused by herpes or chickenpox, bloody diarrhoea, vomiting, pale or yellow skin, weakness, fainting, or urinating less than usual or not at all.

Drugs that are similar
prednisone, acyclovir, Valtrex, Zovirax, Deltasone, lysine, tetracaine topical

Before you take this drug,

If you are allergic to valacyclovir or acyclovir, you shouldn’t take this medicine (Zovirax).

Tell your doctor if you have any of the following:

  • Kidney disease (or if you are on dialysis);
  • Hiv/aids or other conditions that can weaken the immune system;
  • Or a history of kidney transplant or bone marrow transplant.

No one knows if this medicine will hurt a baby who is still in the womb. But an infected mother can give herpes virus to her baby when she gives birth. If you have genital herpes, it is very important to prevent herpes lesions during your pregnancy so that you don’t have a genital lesion when your baby is born.

Valacyclovir can get into breast milk and hurt a baby who is being fed by its mother. If you are breastfeeding, you should tell your doctor.

Don’t give valacyclovir to a child unless a doctor tells you to.

How do I take the medicine valacyclovir?

Take valacyclovir just as your doctor told you to. Follow all of the directions on the label of your medicine. Do not take this medicine in larger or smaller doses, or for longer or shorter periods of time than is recommended.

As soon as possible after the first sign of an infection, start taking valacyclovir (such as tingling, burning, blisters). If you start taking this medicine one or two days after your symptoms started, it might not work as well.

Some herpes infections take longer than others to treat. Use this medicine for as long as your doctor says to. Your symptoms could get better before the infection is gone for good. Skipping doses can make it more likely that your virus will become resistant to the antiviral medicine you are taking.

Valacyclovir can be taken with or without food.

Tell your doctor if your child can’t swallow the valacyclovir tablet while taking this medicine.

While you are taking valacyclovir, you should drink a lot of water to keep your kidneys healthy.

Herpes sores should be kept clean and dry as much as possible. Wearing loose clothes could help keep the lesions from getting worse.

Valacyclovir tablets should be kept at room temperature, away from heat and moisture.

What will happen if I don’t take a dose?

As soon as you remember, take the dose you forgot. If it’s almost time for your next dose, don’t take the one you missed. Do not take more medicine than usual to make up for the dose you missed.

What happens if I overdose?

Get help from a doctor right away or call 1-800-222-1222 to reach the Poison Help line.

What not to do

If you take this medicine, you will still be able to give other people genital herpes. Herpes is contagious, and even if you are taking valacyclovir, you can spread it to other people.

If you don’t want to spread the virus to other people, don’t get sexual or use a latex condom. Don’t let infected parts of your body touch other people. Don’t touch an area that is sick and then touch your eyes. Wash your hands often to stop sickness from spreading.

Do not give your valacyclovir to someone else, even if they have the same symptoms as you.

Valacyclovir side effects

Get medical help right away if you notice any of the following signs of an allergic reaction to valacyclovir: hives; trouble breathing; face, lips, tongue, or throat swelling.

Call your doctor right away if you have:

  • Confusion, aggression, or if you feel shaky or unsteady;
  • Hallucinations (seeing or hearing things that aren’t real);
  • Trouble speaking;
  • A seizure (convulsions); or
  • Kidney problems, such as little or no urination, painful or hard urination, swelling in your feet or ankles, feeling tired or short of breath.

Stop taking valacyclovir and call your doctor right away if you have any of the following serious side effects that can hurt your red blood cells:

  • Fever, pale skin,
  • Unusual bleeding (nosebleeds, bleeding gums),
  • Red or pink urine, little or no urination,
  • Red spots on the skin (not from herpes or chickenpox),
  • Feeling weak or tired,
  • Stomach pain, bloody diarrhoea, vomiting, or
  • Swelling in the face, hands, or feet.

Adults who are 65 or older may be more likely to have side effects.

Some common side effects of valacyclovir are feeling sick/nausea, having stomach pain, or getting a headache.

This isn’t a full list of all possible side effects, and there may be others. You should talk to your doctor about any side effects. You can call 1-800-FDA-1088 to tell the FDA about side effects.

What other medicines might interact with valacyclovir?

Your kidneys can be hurt by valacyclovir. Some medicines, like antivirals, chemotherapy, injected antibiotics, medicine for bowel problems, medicine for high blood pressure, medicine to prevent organ transplant rejection, injectable osteoporosis medicine, and some pain or arthritis medicines, make this effect worse (including Advil, Motrin, and Aleve).

Other drugs, like prescription and over-the-counter medicines, vitamins, and herbal products, may interact with valacyclovir. Tell each of your health care providers about all the medicines you take now and any you start or stop taking.

Questions that are often asked

• If you take valacyclovir instead of acyclovir, what are the benefits?

More about valacyclovir

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Professional resources

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Related treatment guides

• Cold Sores

• Herpes Simplex

• Herpes Simplex, Mucocutaneous/Immunocompetent Host

• CMV Prophylaxis

For more details

Remember to keep this and all other medicines out of the reach of children, to never give your medicines to other people, and to only use valacyclovir for the reason your doctor told you to.

Talk to your doctor or other healthcare provider to make sure that the information on this page applies to your situation.

Medical Disclaimer

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