(Date: August 2015. Version: 2.1)

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 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.

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What is it?

Montelukast (Singulair®) is a medicine used to control the symptoms of asthma. It is usually prescribed to people whose symptoms cannot be controlled by inhalers alone and is taken in the form of granules that are mixed with food.

Is it safe to use montelukast in pregnancy?

No harmful effects on an unborn baby from montelukast use in pregnancy have been identified. However, not enough information is available yet to say for certain that it is safe to use in pregnancy. When deciding whether to take montelukast during pregnancy it is important to weigh up how necessary montelukast is to your health against any possible risks to you or your baby, some of which might depend on how many weeks pregnant you are.

Uncontrolled or poorly controlled asthma in pregnant women has been linked to a number of adverse pregnancy outcomes including stillbirth, preterm birth, and low birth weight in the baby, as well as preeclampsia in the mother. For some women treatment with montelukast in pregnancy might therefore be considered necessary for the wellbeing of both mother and baby. Your doctor is the best person to help you decide what is right for you and your baby.

This leaflet summarises the scientific studies relating to the effects of montelukast on a baby in the womb. 

What if I have already used montelukast 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 using montelukast 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.

None of the three studies that have investigated this have provided strong evidence that babies whose mothers took montelukast in the first trimester of pregnancy are any more likely to have a birth defect than babies of healthy women who did not take montelukast. Together, these studies have investigated birth defect rates in around 500 pregnancies. More research is required to confirm this finding.

Two studies investigated whether a number of specific birth defects were more likely in babies exposed to montelukast in the womb. These studies provided no evidence that montelukast use in early pregnancy increases the chance of the baby having a heart defect or a limb reduction defect (where the arms or legs are shortened or absent).

Can taking montelukast in pregnancy cause miscarriage?

Two small studies found no link between miscarriage and use of montelukast in early pregnancy. More research is required to confirm this finding.

Can taking montelukast in pregnancy cause stillbirth?

A single small study found no strong evidence of a link between stillbirth and use of montelukast in pregnancy. Stillbirth rates need to be studied in more pregnant women using montelukast to confirm this finding.

Can taking montelukast in pregnancy cause my baby to be small at birth (low birth weight)?

Uncontrolled or poorly controlled asthma in pregnancy can affect the way that a baby grows in the womb and montelukast tends to be used for more severe asthma. It is therefore complicated to work out whether montelukast has a specific effect on a baby’s birth weight.

A single study found increased rates of low birth weight in babies of women who used montelukast during pregnancy. However, another study provided evidence that the low birth weight was due to the mother’s asthma rather than montelukast use in pregnancy. Rates of low birth weight in more babies of pregnant women using montelukast need to be studied to determine whether exposure in the womb to montelukast itself can increase the risk of a baby having a low birth weight.

Can taking montelukast in pregnancy cause preterm birth?

Uncontrolled or poorly controlled asthma in pregnancy is a cause of preterm birth. It is therefore complicated to work out whether montelukast use might increase the likelihood of a preterm delivery.

A single study showed that preterm birth was more common in women taking montelukast, but also provided evidence that this was probably due to the women’s asthma rather than the montelukast. More studies need to be carried out to confirm this finding.

Can taking montelukast 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.

There is no known link between montelukast use in pregnancy and learning or behavioural problems (such as ADHD or autism spectrum disorder) in the child later on in life. There are, however, no scientific studies that have specifically investigated a link with these problems.

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. Taking montelukast in pregnancy is not expected to cause problems that would require extra monitoring of your baby.

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

No studies have specifically investigated whether montelukast 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 medicine use in men 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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