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.

Type of medicine Also called
  • Antiviral – a medicine to treat infections caused by viruses.
  • Valtrex®
  • Vaclovir®

What is valaciclovir?

Valaciclovir is a medicine used to treat infections caused by viruses, such as herpes simplex virus (which causes genital herpes) and herpes zoster (which causes shingles). It is also used to prevent viral infections in people with a weakened immune system, eg, if you are receiving cancer medication (chemotherapy) or have had an organ transplant.

Valaciclovir works by stopping viruses reproducing. It does not kill the virus. By taking valaciclovir, your infection will heal more quickly and it will be less severe.

In Aotearoa New Zealand, valaciclovir is available as tablets in two different strengths (500 mg 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 or prevent an infection.  
  • Your doctor will tell you what dose is best for you.
  • Usually the dose ranges from 500 mg to 2 grams taken 1–4 times a day.
  • 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.
  • Timing: 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. 
  • Drink plenty of water while taking valaciclovir. This will keep your kidneys working well. This is especially important for older adults.
  • Missed dose: 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 your course is finished. Do not stop taking it, even if you feel better after a few days. Your doctor will advise you on how long to take valaciclovir for (usually 5–10 days, but it can range from 1 day to 12 months).
  • Wear sunscreen when outside: Protect yourself from too much sunlight while being treated with valaciclovir. Always cover up and apply a thick layer of broad spectrum sunscreen (at least SPF 30) when outside. Do not use sunbeds.

Precautions before taking valaciclovir

  • Are you pregnant or breastfeeding?
  • Do you have kidneys problems?
  • Have you ever had a seizure (fit)?
  • Are you are taking or using any other medicines? This includes any medicines you buy without a prescription, such as herbal and complementary medicines.

If you answered yes to any of these questions, 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.

What are the side effects of valaciclovir?

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?
  • Seizures (fits)
  • Symptoms of easy or unusual bruising or bleeding
  • Tell your doctor immediately or ring Healthline 0800 611 116.
  • Confusion
  • Tell your doctor
  • Nausea (feeling sick) or vomiting
  • Try taking valaciclovir after a meal.
  • Tell your doctor if nausea is bothering you.
  • Headache
  • Tummy pain
  • Diarrhoea (runny poos)    
  • This may settle after a few days.
  • Tell your doctor if this bothers you.
  • 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.
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product


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

Learn more

The following links have more information on valaciclovir. 

Vaclovir Medsafe NZ Consumer Medicine Information
Valaciclovir (tablet) NZ Formulary

Additional resources for healthcare professionals

Antiviral drugs NZ Formulary
Drug induced photosensitivity reactions NZ Formulary
Valtrex Medsafe NZ
Vaclovir Medsafe NZ
Valaciclovir – a first line antiviral medicine BPAC, NZ, 2016

Credits: Sandra Ponen, Pharmacist. Reviewed By: Maya Patel, MPharm PGDipClinPharm, Auckland Last reviewed: 12 Nov 2021