(Date: January 2019. Version: 3)

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.

What is it?

Chlorphenamine (Allercalm®, Hayleve®, Piriton®, Pollenase®) is an antihistamine used to treat hay fever, skin allergies, and other allergic symptoms. It causes drowsiness and is therefore referred to as a sedating antihistamine.

Is it safe to take chlorphenamine in pregnancy?

There is no strong evidence that chlorphenamine is harmful to a baby in the womb. However, because only a small number of pregnant women taking chlorphenamine have been studied, it is not possible to say for certain that it does not affect a baby in some way. When deciding whether or not to take chlorphenamine during pregnancy your doctor will help you to weigh up how necessary chlorphenamine is to your health against the possible risks to you or your baby, some of which will depend on how many weeks pregnant you are.

What if I have already taken chlorphenamine during pregnancy?

If you have taken or are taking 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 if so, to make sure that you are taking the lowest dose that works, and only for as long as you need to.

Can taking chlorphenamine in pregnancy cause birth defects in the baby?

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.

A number of studies have investigated possible links between taking chlorphenamine in the first trimester and specific birth defects. Taken together, the results do not raise alarm that birth defects are caused by use of chlorphenamine in pregnancy. However, only small numbers of women have generally been studied for each type of birth defect; the results of the studies do not all agree and some of the studies did not use the most up-to-date analysis techniques. More research is therefore needed.

Can taking chlorphenamine in pregnancy cause miscarriage?

One very small study found no link between taking chlorphenamine in early pregnancy and miscarriage. While this is reassuring, many more women ideally need to be studied to confirm this finding.

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

No studies have investigated the occurrence of stillbirth, preterm birth (before 37 weeks of pregnancy), or the chance of having a low birth weight baby (<2500 g) in women who took chlorphenamine during pregnancy.

Can taking chlorphenamine in pregnancy cause learning and 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 chlorphenamine.

Will my baby need extra monitoring?

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. Taking chlorphenamine in pregnancy would not normally require extra monitoring of your baby before birth.

Taking chlorphenamine around the time of delivery can cause withdrawal symptoms in the newborn baby as a result of the baby’s body having to adapt to no longer getting chlorphenamine through the placenta. Close monitoring of your baby for a few days after birth may therefore be advised if you have taken chlorphenamine regularly in the weeks before delivery.

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

No studies have specifically investigated whether chlorphenamine used by the father can harm the baby through effects on the sperm, however most experts agree that this is very unlikely. More research on the effects of drug and medicine use in men before and around the time of conception is needed.

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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