Hyperthyroidism can occur during pregnancy and the postpartum period and may affect aspects of breastfeeding, such as milk supply. Antithyroid medication is generally a safe treatment for hyperthyroidism during breastfeeding.

Hyperthyroidism is an overactive thyroid. The thyroid gland, which sits at the front of the neck, makes thyroid hormones, which help control many functions in the body.

With hyperthyroidism, the thyroid gland produces excess thyroid hormones. Without treatment, this can lead to health issues.

After delivering a baby, some people may develop symptoms of hyperthyroidism, which can affect breastfeeding.

This article looks at hyperthyroidism after childbirth (the postpartum period), how it may affect breastfeeding, and how to safely manage both hyperthyroidism and breastfeeding.

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Postpartum thyroiditis is an inflammation of the thyroid gland during the postpartum period that can cause hyperthyroidism, hypothyroidism, or both. It affects around 5 in 100 people during this period.

Postpartum thyroiditis can occur in the first year after delivering a baby in people with no previous history of thyroid disease. This condition may be temporary or permanent.

The presence of certain antibodies, known as thyroid peroxidase (TPO) antibodies, may have a link to postpartum thyroiditis. People with TPO antibodies in the early stages of pregnancy may have a 30% to 52% chance of developing the condition.

If people continue to have TPO antibodies in the third trimester, there is an 80% chance of developing postpartum thyroiditis.

People with hyperthyroidism may experience:

People need normal levels of thyroid hormones for the typical production of milk that breastfeeding requires. Changes in thyroid hormones may cause problems with milk removal.

Some people with postpartum thyroiditis may experience problems with milk supply, but others report no problems.

In some cases of hyperthyroidism, the person can have a large milk supply, while others may have problems with the let-down reflex, which supports the flow of breast milk.

People with hyperthyroidism may require antithyroid medications to reduce thyroid hormone levels. Most of these medications are safe to take while breastfeeding.

According to a 2021 article, it is advisable for people with thyroid dysfunction and taking medication to continue to breastfeed for 6 to 12 months.

The British Thyroid Foundation advises people to take antithyroid medications in small doses two to three times a day after a feed. People should speak with their doctor for the best advice on antithyroid medication dosage.

People may take certain antithyroid medications while breastfeeding to treat hyperthyroidism.

According to a 2021 review, the main treatment for hyperthyroidism is propylthiouracil (PTU), a medication that is safe to take while breastfeeding.

The amount of PTU that enters breast milk is 0.025%. Researchers consider 300 milligrams (mg) or less per day of PTU to be safe while breastfeeding.

Methimazole (Northyx, Tapazole) is also suitable for use while breastfeeding, alongside monitoring the infant’s thyroid function. People may take 20 mg to 30 mg of methimazole per day.

A person can pass hyperthyroidism to their baby during pregnancy if they have Graves’ disease, a common cause of hyperthyroidism.

People with Graves’ disease have certain antibodies that can pass through the placenta and affect the baby. If an infant has these antibodies, they can develop temporary hyperthyroidism, which usually resolves within a few weeks.

No research suggests that a person can pass hyperthyroidism to their baby through breastfeeding.

La Leche League International offers the following advice for breastfeeding with thyroid issues:

  • Attend regular check-ups with a doctor.
  • Talk with a doctor about using an oxytocin nasal spray, as this may improve milk ejection.
  • Massage the breast from the outside toward the nipple to increase the milk supply.
  • Use breast compressions while feeding.
  • If people are able to remove milk and have balanced thyroid levels, consume galactagogues, which are foods to increase the milk supply.
  • If possible, avoid any radioactive treatment until stopping breastfeeding.

Read about some ways to produce more breast milk.

People will need regular checkups with a doctor if they have hyperthyroidism. In people with hyperthyroidism, the breastfed infant will also require monitoring to check growth, development, and thyroid function.

A person should contact a doctor if they have symptoms of hyperthyroidism. Postpartum thyroiditis may cause no symptoms or can result in the following initial symptoms:

People will need to contact a doctor straight away if they are taking antithyroid medication and experience any of the following:

Hyperthyroidism is an overactive thyroid gland and may develop in the postpartum period. Abnormal levels of thyroid hormone may make breastfeeding more difficult by affecting milk supply and removal.

A person should contact a doctor if they have any symptoms of hyperthyroidism. Treatment can help relieve symptoms and prevent complications.

People may take antithyroid medications, which reduce levels of thyroid hormone in the body. Most of these are safe to take while breastfeeding.