Carbimazole: important advice about pregnancy

Last Updated: Monday, 12 October 2026

Carbimazole treats an overactive thyroid by reducing the amount of thyroid hormone your body makes.

The MHRA, the UK medicines regulator, has warned that carbimazole can increase the risk of birth defects if taken during pregnancy, especially during the first 3 months and at higher doses.

What should you do?

• Use effective contraception while taking carbimazole if you could become pregnant. Ask your clinician or pharmacist which method is suitable for you.
• Tell your GP or thyroid specialist straight away if you are planning a baby. Your treatment should be reviewed before you try to become pregnant.
• Contact your GP or thyroid specialist straight away if you think you may be pregnant. Do not wait for a routine appointment.
• Do not stop carbimazole or change your dose without medical advice. An untreated overactive thyroid can also harm you and your baby.

Your specialist will discuss the safest treatment for you. If carbimazole is needed during pregnancy, they will use the lowest effective dose and arrange close monitoring.

Want to discuss your medicine?

Contact your GP practice to book a medication review with a clinician if you have questions about carbimazole, contraception or pregnancy.

Read the full MHRA alert.