You need to be logged in to see the full monograph.


Date of issue: December 2023, Version: 4

bumps logo
A corresponding patient information leaflet on USE OF MEFENAMIC ACID IN PREGNANCY is available.

Mefenamic acid is a non-steroidal anti-inflammatory drug (NSAID) used to treat acute and chronic pain (particularly dysmenorrhoea) and in the management of rheumatoid arthritis. 

The use of NSAIDs in pregnancy has been associated with an increased risk of miscarriage, malformation (including specific defects, such as cardiovascular defects, septal cardiac defects, and orofacial clefts), preterm delivery and fetal growth impairment. However, the available evidence is often conflicting, is likely confounded, and may have also been influenced by methodological limitations. Causal relationships between NSAID use in pregnancy and these outcomes are therefore considered unproven.

Published data regarding the safety of maternal mefenamic acid use in human pregnancy are limited to a placebo-controlled randomised clinical trial which investigated mefenamic acid as a tocolytic in late pregnancy and a population-based cohort study which investigated preterm birth risk among pregnancies with early (before 22 weeks of gestation) mefenamic acid exposure (n>1000 exposures). No adverse fetal effects on gestational length were observed in these studies, and in the former, women receiving mefenamic acid were less likely to deliver preterm than those treated with placebo. Published data regarding other pregnancy outcomes are too limited to provide an adequate assessment of the safety of mefenamic acid use in pregnancy.

Exposure to NSAIDs after 20 weeks of gestation has been associated with an increased risk of premature closure of the ductus arteriosus (DA) and oligohydramnios. These effects are thought to be mediated by the inhibitory effect of NSAIDs on prostaglandin production. There are conflicting findings regarding the risks of persistent pulmonary hypertension of the newborn (PPHN) following antenatal use of NSAIDs. Further evidence is required before this possible association can be confirmed. Where published data regarding the fetal effects of gestational exposure are unavailable or limited, a possible class effect for these associations should be considered for all NSAIDs.

All NSAIDs should, where possible, be avoided after 20 weeks of pregnancy. In circumstances where the maternal clinical condition requires short-term treatment with mefenamic acid (such as acute short-lived pain), treatment should be limited to the shortest duration possible. There is currently no evidence-based guidance about how long use should be restricted for but pragmatic advice is to limit use to no longer than three days. Longer term use, for example for treatment of chronic arthritis, or any use in the third trimester (28 weeks of gestation or beyond), should be avoided. As fetal urine production begins at approximately 10 weeks’ gestational age, UKTIS recommends referral to a Fetal Medicine Unit for monitoring of DA patency and oligohydramnios following prolonged NSAID use after the first trimester.

Where use of mefenamic acid is being considered at any stage of pregnancy, the available pregnancy data should be discussed with the patient to support informed decision-making regarding the risks and benefits of treatment.

Please refer to the NSAID overview monograph for more information. Other risk factors may also be present in individual cases which may independently increase the risk of adverse pregnancy outcome. Clinicians are reminded of the importance of consideration of such factors when performing case-specific risk assessments. Discussion with UKTIS is recommended for all cases of mefenamic acid exposure in pregnancy.

This is a summary of the full UKTIS monograph for health care professionals and should not be used in isolation. The full UKTIS monograph and access to any hyperlinked related documents is available to NHS health care professionals who are logged in.

If you have a patient with exposure to a drug or chemical and require assistance in making a patient-specific risk assessment, please telephone UKTIS on 0344 892 0909 to discuss the case with a teratology specialist.

If you would like to report a pregnancy to UKTIS please click here to download our pregnancy reporting form. Please encourage all women to complete an online reporting form.

Disclaimer: Every effort has been made to ensure that this monograph was accurate and up-to-date at the time of writing, however it cannot cover every eventuality and the information providers cannot be held responsible for any adverse outcomes of the measures recommended. The final decision regarding which treatment is used for an individual patient remains the clinical responsibility of the prescriber. This material may be freely reproduced for education and not for profit purposes within the UK National Health Service, however no linking to this website or reproduction by or for commercial organisations is permitted without the express written permission of this service. This document is regularly reviewed and updated. Only use UKTIS monographs downloaded directly from to ensure you are using the most up-to-date version.