Sounds like 'val-uh-SYE-klo-veer'

Valaciclovir is used to treat infections caused by viruses. Find out how to take it safely and possible side effects. Valaciclovir is commonly called Valtrex or Vaclovir.

Type of medicine Also called
  • Antiviral (to treat infections caused by viruses)
  • Valtrex®
  • Vaclovir®

What is valaciclovir?

Valaciclovir is used to treat infections caused by viruses, such as herpes simplex virus (which causes genital herpes) and herpes zoster (which causes shingles). It works by stopping the growth of the viruses that cause the infection. It reduces the severity of the infection and stops it from spreading. Valaciclovir helps the infection heal faster and lessens pain and itching. Valaciclovir does not kill the virus. The viruses that cause these infections continue to live in your body. Valaciclovir is also used to prevent viral infections in people with a weakened immune system such as if you are receiving cancer medication (chemotherapy) or after organ transplant. Valaciclovir is available as tablets in different strengths (250 milligrams, 500 milligrams and 1 gram).


  • The dose of valaciclovir will be different for different people, depending on the type of infection and whether it is used to treat an infection or prevent an infection.  
  • Your doctor will calculate the dose suitable for you.
  • Usually the dose ranges from 500 milligrams to 2 grams taken 1 to 4 times a day.
  • Your doctor will advise you on how long to take valaciclovir for (usually 5 to 10 days, but it can range from 1 day to 12 months).
  • Always take your valaciclovir exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much valaciclovir to take, how often to take it and any special instructions.

How to take valaciclovir

  • Swallow your valaciclovir tablets with a glass of water.
  • You can take valaciclovir with or without food.
  • Separate your doses out evenly during the day. For example, if your dose is to be taken 4 times a day, take a dose about every 5 hours such as 8am, 1pm, 6pm, and 11pm. Valaciclovir works best when the amount in your body is kept at a constant level.    
  • Drink plenty of water while taking valaciclovir to keep your kidneys working well (unless your doctor advises you otherwise). This is especially important for older adults.
  • If you forget to take your dose, take it as soon as you remember, but, if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.
  • Keep taking valaciclovir until you finish all the tablets. Do not stop taking it, even if you feel better after a few days. 

Precautions – before taking valaciclovir

  • Are you pregnant or breastfeeding?
  • Do you have kidneys problems?
  • Are you are taking or using any other medicines? This includes any medicines you buy without a prescription, such as herbal and complementary medicines.
  • Have you have ever had an allergic reaction to a medicine?

If so, it’s important that you tell your doctor before you start taking valaciclovir. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Possible side effects

Like all medicines, valaciclovir can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Nausea (feeling sick) or vomiting
  • Try taking valaciclovir after a meal.
  • Tell your doctor if troublesome.
  • Headache
  • Stomach pain
  • Diarrhoea (runny poos)    
  • This may settle after a few days.
  • Tell your doctor if troublesome.
  • Feeling sleepy, dizzy or tired
  • Be careful when driving or using tools until you know how this medicine affects you.
  • Signs of an allergic reaction such as skin rash, itching, swelling of your lips, face and mouth or difficulty breathing
  • Tell your doctor immediately or ring HealthLine 0800 611 116.


Valaciclovir may interact with a few medications and herbal supplements, so check with your doctor or pharmacist before starting valaciclovir or before starting any new medicines.

Learn more

The following links have more information on valaciclovir. Be aware that websites from other countries may contain information that differs from New Zealand recommendations.

Vaclovir Medsafe NZ Consumer Medicine Information
Valaciclovir for viral infections Patient Info, UK


  1. Valaciclovir New Zealand Formulary
  2. Valaciclovir – a first line antiviral medicine BPAC, NZ, 2016
  3. Valtrex Medsafe Datasheet
  4. Vaclovir Medsafe Datasheet
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 19 Dec 2018