(Date: October 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?

Olanzapine (Zalasta®, Zyprexa®) belongs to a group of medicines called atypical antipsychotics and is used to treat schizophrenia, mania, and to prevent recurrence of bipolar disorder.

Is it safe to take olanzapine in pregnancy?

When deciding whether or not to take olanzapine during pregnancy it is important to weigh up the potential benefits to your health and wellbeing against the possible risks to you or your baby, some of which will depend on how many weeks pregnant you are. During pregnancy, psychiatric illness can sometimes occur for the first time, or may get worse. For some women, treatment with an antipsychotic such as olanzapine may be offered by a specialist so that they have the best chance of remaining well.

What if I have already taken olanzapine 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.

It is very important that you do not suddenly stop taking olanzapine as this could be dangerous. Do not make any changes to your medication without first talking to your doctor.

Can taking olanzapine 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 total of around 3,000 pregnant women taking olanzapine have been studied. There is currently no suggestion of any link between olanzapine use in pregnancy and general birth defects in the baby.

Additionally, one large study found that babies born to women taking olanzapine were no more likely to have a heart defect than babies born to women not taking olanzapine.

Studies of over 10,000 women who used any type of antipsychotic during pregnancy also do not collectively raise alarm of a link with birth defects.

Can taking olanzapine in pregnancy cause miscarriage?

One small study of 223 women who took olanzapine in pregnancy did not find that they had a higher chance of miscarriage compared to women not taking olanzapine.

Studies of around 3,000 women who used any type of antipsychotic during pregnancy do not raise concern of a direct link with miscarriage. While this is reassuring, further studies of women specifically taking olanzapine are ideally required.

Can taking olanzapine in pregnancy cause stillbirth?

One study of 610 women who had taken olanzapine in pregnancy found that they did not have a higher chance of stillbirth than women in the background population.

Studies of stillbirth in pregnant women taking any antipsychotic have produced mixed findings, with three studies finding no link but one large study finding a possible link. Further studies of women specifically taking olanzapine are required before definite conclusions can be drawn.

Can taking olanzapine in pregnancy cause preterm birth?

One study of 610 women who had taken olanzapine in pregnancy found that they did not have a higher chance of preterm delivery than women in the background population.

Some (but not all) studies of pregnant women taking any antipsychotic have shown a possible link with preterm delivery, but it is thought that lifestyle factors in pregnant women taking antipsychotics are likely to have contributed to this finding. Because there is only one study of women specifically taking olanzapine, more information on this subject is needed.

Can taking olanzapine in pregnancy affect a baby’s growth in the womb and his/her birth weight?

Low birth weight
No studies have investigated whether olanzapine use in pregnancy might affect a baby’s birth weight. Studies of pregnant women taking any antipsychotic do not overall raise alarm that their use slows the baby’s growth in the womb. Information about women specifically taking olanzapine ideally needs to be collected.

Increased birth weight
Weight gain, high blood sugar and diabetes are common side effects of antipsychotic use in non-pregnant individuals. If these problems occur in pregnancy they can in turn cause increased growth of a baby in the womb. Some studies, but not others, have found a possible link between antipsychotic use in pregnancy and having a large baby. However, no studies have yet investigated whether babies born to women specifically taking olanzapine are more prone to having a high birth weight.

Can taking olanzapine in pregnancy cause other health problems in the child?

Withdrawal symptoms at birth (neonatal withdrawal)
Withdrawal symptoms are thought to occur as the newborn baby’s body has to adapt to suddenly no longer getting certain types of medicines through the placenta.

Taking olanzapine and other antipsychotics during pregnancy can lead to neonatal withdrawal. Close monitoring of your baby for a few days after birth may therefore be advised if you have taken olanzapine regularly in the weeks before delivery. Your doctor may therefore advise that your baby is delivered at a hospital with facilities to provide this care.

Learning and behavioural problems
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 investigated learning and behaviour in children exposed in the womb to olanzapine.

Will my baby need extra monitoring?

Most women will be offered a scan at around 20 weeks of pregnancy to look for birth defects and check their baby’s growth as part of their routine antenatal care. Taking olanzapine in pregnancy would not normally require extra monitoring of your baby. 

Weight gain and increased blood sugar (hyperglycaemia) can be side effects of olanzapine. If you are taking olanzapine during pregnancy and are gaining more weight than expected, or have higher than expected levels of sugar in your urine, your doctor may offer you a glucose tolerance test to measure how your body responds to sugar.

If you have taken olanzapine around the time of delivery your baby may require extra monitoring after birth because of the possible risk of neonatal withdrawal.

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

We would not expect any increased risk to your baby if the father took olanzapine 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 www.uktis.org.  

Feedback request 

WE NEED YOUR HELP! Do you have 3 minutes to complete a short, quick and simple 12 question user feedback form about our bumps information leaflets? To have your say on how we can improve our website and the information we provide please visit here.

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.

My bump’s record

Create your own ‘My bump’s record’.

Provide information about your pregnancy to help women in the future.

Login to my bumps

Join my bumps