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December 08, 2022 4 min read

Breastfeeding is one of the most natural and beautiful things a mother can do for her child. But what happens when you have thyroid disease and need to take medication? Can you still breastfeed while taking levothyroxine? Read on to learn everything you need about levothyroxine, hypothyroidism, and breastfeeding!

What is the thyroid, and what are the main thyroid disease?

The thyroid is a butterfly-shaped gland on your neck. Its primary function is to produce two hormones: thyroxine (T4) and triiodothyronine (T3). Thyroid hormones play a vital role in regulating the body’s metabolism. Your thyroid work with the pituitary gland, a small gland at the base of the brain. The pituitary gland makes a hormone called stimulating thyroid hormone (TSH). TSH tells the thyroid how much hormone it needs to make.

If your thyroid function is impaired, either it produces too much or too little hormones, it can cause problems with how your body works. There are two main types of thyroid disease: hypothyroidism and hyperthyroidism. Hypothyroidism (underactive thyroid) is a thyroid disease that occurs when your thyroid gland is not making enough hormone. On the other hand, hyperthyroidism (overactive thyroid) means that your thyroid gland is producing too much hormone. 

A small percentage of pregnant women experience postpartum thyroiditis, which is a condition when your thyroid gland becomes inflamed after you have a baby. This condition may first cause hyperthyroidism, but over time, it can lead to hypothyroidism.

To test postpartum thyroiditis, doctors may use radioactive iodine, which isn't safe for pregnant and breastfeeding women. Therefore, make sure to let your doctor know and ask them when it's safe to resume breastfeeding after a test.

Can underactive thyroid affect breast milk production?

One of the main ways thyroid hormones stimulate breast milk production is by stimulating the release of prolactin from the pituitary gland. Prolactin is a hormone that is responsible for milk production. In addition to stimulating prolactin release, the hormones of the thyroid also increase the amount of milk produced and help regulate breast milk's composition. 

That’s why thyroid issues can cause difficulties with milk removal. And if you have low thyroid hormone levels while breastfeeding, you may find that your milk production is either delayed or insufficient.

If the mother has hypothyroidism, will it affect the baby?

When hypothyroidism or an autoimmune thyroid disease associated with hypothyroidism is untreated, the low milk supply may cause your baby to experience poor weight gain.

Is it safe for a mom to breastfeed with hypothyroidism?

Since hypothyroidism can cause low milk production, it can be challenging to breastfeed your baby. But don’t worry; it’s safe for a mom with hypothyroidism to breastfeed her baby. However, it’s vital that you get correctly treated for hypothyroidism.

How is hypothyroidism treated?

Hypothyroidism is usually treated by replacing the amount of thyroid hormone your body is not producing. For breastfeeding mothers, most doctors will prescribe an oral thyroid hormone replacement called levothyroxine (Synthroid, Levoxyl, Tirosint, Unithroid). It’s a synthetic version of T4.

Levothyroxine works by replacing the missing hormone in the body. Thus, you’ll have a normal range of thyroid levels, which is important for normal lactation and maintaining a sufficient supply of milk.

Is it safe to take thyroid hormone medication while breastfeeding?

As a breastfeeding mother, the idea of taking thyroid medications while breastfeeding can make you uncomfortable.

The good news is that taking thyroid hormone medications like levothyroxine while breastfeeding is safe. The synthetic form of T4 in levothyroxine is the same as the natural hormone in your body.

Remember, your body needs healthy thyroid hormone levels to produce enough milk for your baby. This means that if you take levothyroxine, you likely won’t have any problems with your milk supply anymore.

The key is to take the exact dose prescribed by your doctor. When you take too little, producing milk will still be hard. Conversely, too much can cause your thyroid levels to become too high. This can be dangerous for you and your baby.

Can underactive thyroid affect breast milk production?

Can thyroid medication affect breast milk?

Breast milk frequently contains thyroid hormones. And when you take levothyroxine, only extremely low levels of the drug will pass into your milk.

The predicted exposure level for your baby is 0.6 nanograms per kilogram per day, which is essentially undetectable. This amount is not enough to affect or harm your baby. It won’t influence tests for neonatal hypothyroidism (an underactive thyroid in babies).

Again, you must take the right dose of levothyroxine. Make sure to monitor your baby for any changes in behavior or development if you take levothyroxine while breastfeeding. If you have any worries, be sure to talk to your doctor.


Thyroid hormones are important for your milk supply, so having a thyroid disease may interfere with its production. When you have low thyroid levels in your body, it might be difficult for you to produce enough milk for your baby. Without enough milk supply, your baby might experience poor weight gain and low energy.

That’s why taking levothyroxine to balance the thyroid levels in your body is important. When your thyroid levels are normal, you’ll likely produce enough breastmilk for your baby. It’s okay to have concerts, but it’s important to remember that taking levothyroxine while breastfeeding is fine.

Wojciech Majda
Wojciech Majda

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