(Date: August 2019. Version: 2)

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 Public Health England 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.

What is it?

Allopurinol (Uricto®, Zyloric®) is a medicine that is used in people with gout, kidney stones, inflammatory bowel disease, certain types of parasite infection, and may also be given following a kidney transplant.

Is it safe to take allopurinol in pregnancy?

When deciding whether to take allopurinol during pregnancy it is important to weigh up how necessary allopurinol is to your health against any possible risks to you or your baby, some of which may depend on how many weeks pregnant you are. Your doctor is the best person to help you decide what is right for you and your baby.

What if I have already taken allopurinol during pregnancy?

If you have taken any medicines it is always a good idea to let your doctor know that you are pregnant so that you can decide together whether you still need the medicines that you are on and to make sure that you are taking the lowest dose that works.

Can taking allopurinol in pregnancy cause my baby to be born with birth defects?

A baby’s body and most internal organs are formed during the first 12 weeks of pregnancy. It is mainly during this time that some medicines are known to cause birth defects.

Only 43 babies born to women who took allopurinol during the first twelve weeks of pregnancy have been written about in scientific journals with respect to whether they had birth defects.  

Forty-one of these babies did not have birth defects, but two had a similar and distinctive pattern of birth defects (including cleft lip and palate, and abnormalities of the ear, eye, kidney, brain and genitals). While it is clear that the majority of babies exposed in the womb to allopurinol were born without birth defects, these two reports raise the possibility that allopurinol can cause problems in a small number of cases. Before we can be sure, more pregnant women who have taken allopurinol need to be studied.

If you have been prescribed allopurinol in early pregnancy it is best to discuss any concerns that you have with your doctor who will be able to help you weigh up the possible risks and benefits of treatment.

Can taking allopurinol in pregnancy cause miscarriage?

A small study of a group of 31 pregnant women taking allopurinol did not raise concern of any link with miscarriage. However, because the chance of miscarriage has been studied in so few women taking allopurinol, much more research is required to confirm this finding.

Can taking allopurinol in pregnancy cause stillbirth?

The small amount of available information does not suggest that taking allopurinol during pregnancy causes stillbirth, but much more research is needed to confirm this.

Can taking allopurinol in pregnancy cause preterm birth, or my baby to be small at birth (low birth weight)?

The available information does not raise alarm that taking allopurinol during pregnancy causes preterm birth (before 37 weeks) or low birth weight (<2,500 g). However, these outcomes have been studied in only a very small number of babies exposed to allopurinol in the womb and more research is therefore required.

Can taking allopurinol in pregnancy cause learning or behavioural problems in the child?

A baby’s brain continues to develop right up until the end of pregnancy. It is therefore possible that taking certain medicines at any stage of pregnancy could have a lasting effect on a child’s learning or behaviour.

No studies have assessed learning and behaviour in children exposed in the womb to allopurinol.

Will my baby need extra monitoring during pregnancy?

Most women will be offered a scan at around 20 weeks of pregnancy to look for birth defects as part of their routine antenatal care. Because there is a possibility that allopurinol taken in early pregnancy increases the chance of birth defects, your doctor may offer you more detailed ultrasound scans. Additionally, some of the illnesses that allopurinol is used to treat are themselves reasons for a woman to have her pregnancy monitored more closely.

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

We would not expect any increased risk to your baby if the father took allopurinol before or around the time you became pregnant.

Who can I talk to if I have questions?

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

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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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