Mefenamic acid

(Date: March 2019. Version: 3.0.1)

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.

Updated guidance (2023)

PLEASE BE AWARE: The advice about use of NSAIDs in pregnancy has recently changed. It is now recommended that prolonged use of NSAIDs should be avoided after 20 weeks of pregnancy (rather than the 30 weeks discussed throughout this document). For more information, please see the information here. We will be updating this document as soon as possible to include the new advice.

Mefenamic acid - What is it?

Mefenamic acid (Ponstan®) is a type of painkiller that your doctor may prescribe to treat pain caused by arthritis, a recent operation, or heavy periods. It belongs to a class of drug called non-steroidal anti-inflammatory drugs (NSAIDs). This leaflet summarises the scientific studies relating to the effects of mefenamic acid on a baby in the womb.

Use of mefenamic acid during pregnancy is not advised unless prescribed by a doctor, especially if you are 30 or more weeks pregnant. Paracetamol is usually recommended to control pain or fever during pregnancy. If paracetamol does not control your pain it is important that you ask your doctor for advice before taking mefenamic acid or any other NSAID. Mefanamic acid may be prescribed during pregnancy for some women with certain illnesses; women who need to take mefenamic acid after 30 weeks of pregnancy will be monitored by a fetal medicine specialist.

What if I have already taken mefenamic acid during pregnancy?

Taking mefenamic acid before week 30 of pregnancy is unlikely to harm a baby in the womb. However, 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 medication.

If you have taken mefenamic acid after week 30 of pregnancy it is important that you let your doctor or midwife know as soon as possible.

Can taking mefenamic acid in pregnancy cause miscarriage?

It is unclear whether taking mefenamic acid in early pregnancy could increase the chance of miscarriage. No studies have investigated the likelihood of miscarriage in women specifically taking mefenamic acid. Some studies have, however, shown that women who take any type of NSAID during pregnancy are more likely to have a miscarriage than women who do not.

Can taking mefenamic acid 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.

No studies have assessed the chance of birth defects in babies born to women who specifically took mefenamic acid in early pregnancy. Current information does not raise alarm that birth defects are caused by general use of NSAIDs in pregnancy, although ongoing research is needed.

What problems can taking mefenamic acid after 30 weeks of pregnancy cause in my baby?

Premature closure of the ductus arteriosus
Before birth, a blood vessel in the baby called the ductus arteriosus needs to stay open to supply the baby in the womb with nutrients and oxygen from the mother. The ductus arteriosus closes after birth. ‘Premature closure of the ductus arteriosus’ is the medical term used to describe this blood vessel closing before it is supposed to.

Taking mefenamic acid or another NSAID after 30 weeks of pregnancy can cause the ductus arteriosus to close while the baby is in the womb. It is important to contact your doctor or midwife straight away if you have taken an NSAID after 30 weeks of pregnancy, especially if you have taken several doses, or more than the recommended dose.

Persistent pulmonary hypertension of the newborn (PPHN)
PPHN occurs when a newborn baby’s lungs do not adapt to breathing outside the womb. It is thought to be linked, in some cases, to early closure of the ductus arteriosus (see above). PPHN is generally rare but it can be serious.

Although two small studies have shown a link between PPHN and taking NSAIDs during pregnancy, another larger study did not show a link. Further research is required to assess the chance of PPHN following exposure in the womb to NSAIDs and specifically to mefenamic acid.

Oligohydramnios (reduced fluid around the baby)
Use of mefenamic acid or other NSAIDs after 30 weeks of pregnancy may result in oligohydramnios (where there is too little amniotic fluid in the sac around the baby).

Mefenamic acid should only be taken after week 30 of pregnancy under medical supervision. If you have taken mefenamic acid after 30 weeks of pregnancy your obstetrician may wish to check the baby (and amniotic fluid levels) by ultrasound scan.

Can taking mefenamic in pregnancy cause stillbirth?

A small study did not raise alarm that use of mefenamic acid in pregnancy causes stillbirth. Two studies of women taking any NSAID in pregnancy did not show a link with stillbirth.

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

There is no evidence that use of any NSAID in pregnancy causes preterm delivery or low infant birth weight.

Can taking mefenamic acid 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 mefenamic acid.

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 mefenamic acid before 30 weeks of pregnancy would not normally require extra monitoring of your baby.

If you have taken mefenamic acid after 30 weeks of pregnancy, extra scans to monitor the wellbeing of your baby are likely to be needed. Discuss this with your midwife/obstetrician.

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

We would not expect any increased risk to your baby if the father took mefenamic acid before or around the time your baby was conceived.

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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