(Date: July 2022. Version: 3.1)

This factsheet has been written for members of the public by the UK Teratology Information Service (UKTIS). UKTIS is a not-for-profit organisation funded by the UK Health Security Agency (UKHSA) on behalf of UK Health Departments. UKTIS has been providing scientific information to health care providers since 1983 on the effects that medicines, recreational drugs and chemicals may have on the developing baby during pregnancy.

Quick read

Aciclovir can be used in pregnancy and is the first-choice treatment for cold sores, genital herpes and, occasionally, chickenpox.

What is it?

Aciclovir cream (Zovirax®) is used to treat cold sores and can be bought over the counter. Aciclovir in tablet form is used to treat and prevent genital herpes and chickenpox.

What are the benefits of using aciclovir in pregnancy?

Aciclovir cream can help to speed up healing of cold sores and reduces symptoms such as burning and pain.

Aciclovir tablets can prevent genital herpes from flaring during later pregnancy and being passed on to the baby during delivery.

Aciclovir tablets can also reduce the severity of a chickenpox infection. Treatment with aciclovir can also reduce the risk of a pregnant woman who has not had chickenpox from developing the illness following contact with an infected person.

What are the risks of using aciclovir in pregnancy?

There are no known risks of using aciclovir in pregnancy. Aciclovir cream does not enter the bloodstream in levels that are high enough to affect the baby.

Are there any alternatives to using aciclovir in pregnancy?

Possibly. Other antiviral medicines are available but aciclovir is usually the first-choice in pregnancy as it is considered to be the safest option.

Some women may choose not to treat uncomplicated facial cold sores in pregnancy and these usually get better within a few days.

Paracetamol can be used to safely treat symptoms that may be linked to a cold sore, including achy joints, a temperature, and pain.

What if I prefer not to take medicines during pregnancy?

Use of aciclovir in pregnancy for genital herpes can reduce the chance of preterm delivery and prevent the baby catching herpes during delivery, which can lead to serious complications.

Use of aciclovir to treat or prevent chickenpox is important because chickenpox can cause complications in adults and, especially in early pregnancy, can harm the unborn baby.

A doctor or midwife will be happy to discuss any concerns about using aciclovir in pregnancy.

Will my baby need extra monitoring?

As part of routine antenatal care in the UK, women are invited for a very detailed scan at around 20 weeks of pregnancy to check the baby’s development. Using aciclovir in pregnancy is not expected to cause problems that would require any extra monitoring.

Are there any risks to my baby if the father has taken aciclovir?

We would not expect any increased risk to the baby if the father used aciclovir before or around the time of conception.

Who can I talk to if I have questions?

If you have any questions about the information in this leaflet please discuss them with your health care provider. They can access more detailed medical and scientific information from

How can I help to improve drug safety information for pregnant women in the future?

Our online reporting system allows women with a current or previous pregnancy to create a digitally secure ‘my bumps record’. You will be asked to enter information about your health, whether or not you take any medicines, and your pregnancy outcome. You can update your details at any time during pregnancy or afterwards. This information will help us better understand how medicines affect the health of pregnant women and their babies. Please visit to register.

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General information 

Up to 1 out of every 5 pregnancies ends in a miscarriage, and 1 in 40 babies are born with a birth defect. These are referred to as the background population risks.  They describe the chance of these events happening for any pregnancy before taking factors such as the mother’s health during pregnancy, her lifestyle, medicines she takes and the genetic make up of her and the baby’s father into account.

Medicines use in pregnancy

Most medicines used by the mother will cross the placenta and reach the baby. Sometimes this may have beneficial effects for the baby.  There are, however, some medicines that can harm a baby’s normal development.  How a medicine affects a baby may depend on the stage of pregnancy when the medicine is taken. If you are on regular medication you should discuss these effects with your doctor/health care team before becoming pregnant.

If a new medicine is suggested for you during pregnancy, please ensure the doctor or health care professional treating you is aware of your pregnancy.

When deciding whether or not to use a medicine in pregnancy you need to weigh up how the medicine might improve your and/or your unborn baby’s health against any possible problems that the drug may cause. Our bumps leaflets are written to provide you with a summary of what is known about use of a specific medicine in pregnancy so that you can decide together with your health care provider what is best for you and your baby.   

Every pregnancy is unique. The decision to start, stop, continue or change a prescribed medicine before or during pregnancy should be made in consultation with your health care provider. It is very helpful if you can record all your medication taken in pregnancy in your hand held maternity records.

Disclaimer: This information is not intended to replace the individual care and advice of your health care provider. New information is continually becoming available. Whilst every effort will be made to ensure that this information is accurate and up to date at the time of publication, we cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes following decisions made on the basis of this information. We strongly advise that printouts should NOT be kept for any length of time, or for “future reference” as they can rapidly become out of date.

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