Aciclovir (tablets)

Sounds like 'ay-SYE-kloe-vir'

Aciclovir tablets are used to treat viral infections. Find out how to take them safely and possible side effects.

Type of medicine Also called
  • Antiviral – medicine to treat infections caused by viruses
  • Lovir®
  • Zovirax®

What is aciclovir?

Aciclovir is used to treat infections caused by viruses, such as herpes simplex virus (which causes cold sores around your mouth and genital herpes) and varicella zoster (which causes chickenpox and shingles). It is also used to prevent viral infections in people with a weakened immune system, eg, if you are receiving cancer medicine (chemotherapy).

Aciclovir works by stopping viruses reproducing. It does not kill the virus. By taking aciclovir, your infection will heal quicker and it will be less severe.

In Aotearoa New Zealand, aciclovir is available as tablets in different strengths (200 mg, 400 mg and 800 mg).


  • The dose of aciclovir 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 200 mg to 800 mg and is taken 2–5 times a day.
  • For most infections, you should start to feel better after taking aciclovir for a few days.
  • Always take your aciclovir exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much aciclovir to take, how often to take it and any special instructions.

How to take aciclovir

  • Swallow your aciclovir tablets with a glass of water. If you have difficulty swallowing the tablet, the tablet can be dissolved in a small glass of water. Stir until dissolved. Drink all the water to make sure you get the full dose.
  • Timing: Separate your doses out evenly during the day. For example, if your dose is to be taken 5 times a day, take a dose about every 4 hours such as 7am, 11am, 3pm, 7pm and 11pm. You can take aciclovir with or without food.     
  • Drink plenty of water while taking aciclovir. It's important to drink plenty of water so you don't get dehydrated while taking aciclovir. This could affect your kidneys. 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 aciclovir until the 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 aciclovir for (usually 5–10 days).
  • Wear sunscreen when outside. Protect yourself from too much sunlight while being treated with aciclovir. 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 aciclovir

  • Are you pregnant or breast-feeding?
  • Do you have any kidneys problems?
  • Have you ever had a seizure (fit)?
  • Are you taking 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 aciclovir. 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 aciclovir (tablets)?

Like all medicines, aciclovir 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 aciclovir after a meal.
  • Tell your doctor if nausea continues to bother you.
  • Stomach pain
  • Diarrhoea (runny poos)    
  • Drink lots of fluids.
  • This may settle after a few days.
  • Tell your doctor if it is bothering you.
  • Headache, 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 of a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product


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

Learn more

The following links have more information on aciclovir. 

Lovir Medsafe NZ Consumer Medicine Information
Aciclovir (tablet) NZ Formulary

Additional resources for healthcare professionals

Antiviral drugs NZ Formulary
The diagnosis and management of herpes zoster and its complications BPAC, NZ, 2014
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