What is Valacyclovir used for?

What you need to know about one of the most popular herpes medications.


Valacyclovir (Valtrex, Zelitrex) is an antiviral drug used to treat viral infections caused by herpes simplex (cold sores, genital herpes), herpes zoster (shingles) and varicella zoster (chickenpox).


What is Valacyclovir used for?

Valacyclovir is commonly used to treat herpes outbreaks and minimize the occurrence of herpes in the future. There is no cure for infections caused by the herpes simplex virus type 1 (HSV 1) and type 2 (HSV 2), but symptoms can usually be managed with antiviral medications.

If you have herpes or chickenpox, it’s likely you may be prescribed valacyclovir or a similar antiviral drug. The dosage and length of your treatment will be dependent on the type of virus.

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For genital herpes and cold sores, adults are usually prescribed 1g of the medication twice a day for up to 10 days.

The drug can be used to suppress symptoms and herpes outbreaks by taking 500mg to 1g once a day.

To treat herpes zoster, adults are usually recommended a dose of 1g 3 times a day for up to 7 days.

If you’re not sure how to take valacyclovir, consult the patient information leaflet or speak to a healthcare advisor.


How does Valacyclovir work?

The antiviral medicine works by preventing the herpes virus from multiplying and spreading. Once inside the cell, the medication’s active ingredient acyclovir reduces the replication of the virus. As a consequence, HSV does not spread to healthy cells.


Valacyclovir has been tested extensively in clinical trials and observational studies. Research has repeatedly shown that the drug is safe even when used long-term at doses up to 1g a day.


Whilst the prescription drug reduces the severity of HSV-1 and HSV-2, it does not cure herpes. It is used to help heal open sores faster and relieve associated symptoms such as aches and pains.


But valacyclovir can be taken to reduce the risk of viral shedding and transmission of HSV. One study found that 1g daily reduced recurrences of genital herpes in 79% of participants compared to 52% of people taking a placebo.


It’s important to understand that carriers of HSV are infectious at all times and even though valacyclovir can reduce viral shedding, patients must use a condom during sexual intercourse (HSV-2) and avoid kissing (HSV-1) if they have any open mouth sores.


When will Valacyclovir start working?

How quickly you will notice a relief of your symptoms depends on the severity of your infection and the time at which you started your treatment.


In most cases, the drug will act rapidly and you should see a reduction in the severity of your herpes symptoms within 48 hours. It’s best to take valacyclovir as soon as you notice any signs to make sure recovery is rapid.


When it comes to herpes, the first outbreak will often be the worst, which means it could take longer for valacyclovir to work. Subsequent outbreaks can be less severe and the medicine should work faster.


How long does Valacyclovir stay in your system?

Once inside the human body, valacyclovir converts into its active ingredient acyclovir. Drugs that convert to be metabolized are called prodrugs. They are often more bioavailable, which means that more of the drug is available to be used by the body for treatment.


Valacyclovir has a half-life of around 3 hours once converted to acyclovir. In other words, it takes 3 hours for a dose of 500mg to reduce to half of its value.


Valacyclovir side effects

Common side effects of valacyclovir include:

  • Headache
  • Nausea and vomiting
  • Dizziness
  • Stomach and/or joint pain
  • Skin rash
  • Depression


If you notice any of the following symptoms seek emergency medical help as it could indicate an allergic reaction to acyclovir:


  • Confusion or hallucination
  • Feeling shaky
  • Speech problems
  • Seizures
  • Pain in the kidneys
  • Fever
  • Abnormal bleeding
  • Abnormal coloration of urine
  • Blood in the stool
  • Swelling of the hands, feet or face



Valacyclovir is one of the most commonly used herpes treatments. If you have cold sores (HSV-1) or genital herpes (HSV-2), it’s likely your doctor will prescribe valacyclovir.


The drug is often sold as Valtrex or Zelitrex but many generic versions are available.


When dealing with herpes, it’s important to follow your doctor’s or healthcare provider’s advice.



  1. Valacyclovir Dosage. Retrieved November 1, 2019, from website:
  2. Tyring, S. K., Baker, D., & Snowden, W. (2002). Valacyclovir for Herpes Simplex Virus Infection: Long?Term Safety and Sustained Efficacy after 20 Years’ Experience with Acyclovir. The Journal of Infectious Diseases, 186(s1), S40–S46.
  3. Bonnar P. E. (2009). Suppressive valacyclovir therapy to reduce genital herpes transmission: good public health policy?. McGill journal of medicine : MJM : an international forum for the advancement of medical sciences by students, 12(1), 39–46.
  4. Martens, M. G., Fife, K. H., Leone, P. A., Dix, L. P., & Brennan, C. A. (2009). Once Daily Valacyclovir for Reducing Viral Shedding in Subjects Newly Diagnosed with Genital Herpes. Infectious Diseases in Obstetrics and Gynecology, 2009, 1–7.
  5. Valtrex. (2018, October 25). Retrieved November 1, 2019, from RxList website:

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