Thyroid UK
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Breastfeeding on carbimazol

Hi there!

I'm taking 5mg of carbimazol twice a day and I'm still breast feeding. I would be interested to find out if there is anyone else doing the same! I've been advised by my gp and more than one doctor at a local hospital to stop breastfeeding immediately. After hours of searching online, speaking to breastfeeding experts and someone who works in pharmaceuticals, I've found out it's not harmful to the child in such small doses. Having conflicting advice is confusing and obviously I don't want any harm to come to my child and I have tried to wean her off feeding, but it's so stressful for her and me.

Any advice welcome

2 Replies

I am sorry that you are in a predicament. No matter what the experts have told you, you must still worry. I have read two articles and this is an excerpt from both:-

This medicine should be used with caution during pregnancy, and only if the expected benefit is greater than its possible risks to the developing baby. Your doctor can give you further information and advice about this. Tell your doctor straight away if you think you could be pregnant while taking this medicine.

This medicine passes into breast milk in small amounts. The manufacturer recommends that mothers who are receiving treatment with this medicine should not breastfeed their infants. However, various studies have suggested that small doses taken by the mother do not appear to pose a major risk to a nursing infant, provided the baby's development and thyroid function are closely monitored. Get medical advice from your doctor before breastfeeding if you are taking this medicine.

Carbimazole is not approved for marketing in the United States by the US Food and Drug Administration, but is available in other countries. It is a prodrug for methimazole which has been studied extensively during breastfeeding; maternal methimazole therapy does not affect thyroid function or intellectual development in breastfed infants with doses up to 20 mg daily. Doses of carbimazole of 30 mg daily or 50 mg weekly have not adversely affected the few breastfed infants studied. In general, antithyroid drugs should be given in divided doses taken right after nursing.[1] Rare idiosyncratic reactions (e.g., agranulocytosis) might occur, and the infant should be watched for signs of infection. Monitoring of the infant's complete blood count and differential is advisable if there is a suspicion of a drug-induced blood dyscrasia. Some authors have recommended routine monitoring of the breastfed infant's thyroxine (T4) and thyrotropin (TSH) during maternal propylthiouracil use at 3 to 4 weeks of age.[1][2][3][4] However, no case of thyroid function alteration has been reported among infants exposed to methimazole via breastmilk and other sources state than routine monitoring of thyroid function is unnecessary.[5]


That's great thanks for spending the time to respond. Both articles are very interesting and reassuring.


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