Taking Thyroid Medication While Breastfeeding

Both thyroid hormone replacement and antithyroid drugs are safe

A breastfeeding mother needs to be mindful of anything she uses that could pass through her milk to her baby, and it's natural to wonder if that means thyroid medications, too. While the only way to be certain about the safety of taking any medication while nursing is to discuss it with your healthcare provider, it's generally considered that drugs used to treat hypothyroidism and hyperthyroidism are OK to take when used as directed—which may involve some modification to your current regimen. The type of thyroid disease you have, the specific medication you take, and the dosage should all be considered by your healthcare provider.

Under-treated hypothyroidism and hyperthyroidism can have consequences, both to your health and your breastfeeding efforts, so it's important to manage your condition in a way that's both effective for you and safe for your nursing child.

mother reading pill bottle label while holding baby
Ariel Skelley / Getty Images

Hypothyroid Medications and Breastfeeding

While there are definitely medications that are ill-advised for nursing mothers, thyroid hormone replacement drugs used to treat an underactive thyroid (hypothyroidism), including Hashimoto's disease, are exceptions.

Stopping your hypothyroidism medication may cause your thyroid levels to drop, prompting you to experience symptoms of your condition. Even taking a lower dose (without your healthcare provider's guidance) could affect your symptoms.

The medications most often prescribed for hypothyroidism include:

  • Generic levothyroxine
  • Brand-name levothyroxine: Levothroid, Levo-T, Levoxyl, Synthroid, Tirosint, and Unithroid
  • Cytomel (L-triiodothyronine)

If the idea of taking one of these while nursing makes you uncomfortable, it may be helpful to know that hormone replacement medications are the same as the natural thyroid hormones produced in the body.

What's more, as long as you stick to the prescribed dosage for you—that is, the amount that will keep your thyroid hormones at a normal level—only very small quantities of the drug will pass into your breast milk. The amount will not be enough to have an adverse effect on your baby.

Equally important, adequate thyroid hormone is necessary for normal lactation and for maintaining a sufficient supply of breastmilk. In fact, without your thyroid medication, you may not be able to breastfeed.

It's entirely possible to take too much thyroid replacement medication, which could bring on symptoms of hyperthyroidism. Again, make sure you're taking the exact dose prescribed by your healthcare provider.

Note, too, that natural desiccated thyroid hormone (often prescribed by alternative medicine practitioners and sold under names such as Armour Thyroid and Nature-Throid) are not recommended for women of childbearing age. If you take one of these, talk to your healthcare provider about switching your medication.

Hypothyroidism Post-Pregnancy

Your hormone levels may fluctuate during and after pregnancy. This makes it possible to develop hypothyroidism for the first time or, if you've been diagnosed and effectively managing your condition, to experience changes in hormone levels that lead to symptoms.

Many of the symptoms of hypothyroidism mimic those of postpartum fatigue, postpartum depression, and even breastfeeding itself, so you may be inclined to write them off as normal. However, if you have any of the following and if you're having trouble breastfeeding and producing milk, let your healthcare provider know. If testing reveals that you've developed hypothyroidism, or that your levels are out of the normal range again, prompt treatment with hypothyroid medication (or a dose adjustment) should relieve your symptoms and allow you to continue nursing successfully:

  • Fatigue
  • Decreased appetite
  • Depression
  • Cold intolerance
  • Thinning hair
  • Dry skin
  • Hoarse voice 

Hyperthyroid Medications and Breastfeeding

The medications used to treat hyperthyroidism, as well as the autoimmune condition Graves' disease, are designed to lower above-normal levels of thyroid hormone.

For some time, women taking so-called antithyroid drugs— propylthiouracil (often referred to as PTU), Tapazole (methimazole), and, in Europe, carbimazole (which converts to methimazole in the body)—were discouraged from breastfeeding. The concern was that the medication would pass through breastmilk and suppress the baby's thyroid gland or cause an enlargement of the gland known as goiter.

In recent years, however, research has determined that in general, antithyroid drugs taken by women who are breastfeeding aren't likely to harm their infants or to affect the babies' thyroid or physical or intellectual development. There are some precautions, however.

A 2012 study published in the European Thyroid Journal, for example, determined specific safe doses of antithyroid medication:

  • Propylthiouracil: Up to 300 milligrams (mg) per day
  • Methimazole: Up to 30 mg per day
  • Carbimazole: Up to 15 mg per day

However, because propylthiouracil is linked to a small risk of liver damage, the researchers advise that it should only be used in special cases and for very short periods of time. What's right for you, of course, should be taken up with your healthcare provider.

A Word From Verywell

If you have thyroid disease that you take medication for, in all likelihood it won't harm your baby—and it's critical for your health and likely even your ability to breastfeed. Just to be safe, it's advisable to nurse your little one before you pop your pill. This way the drug will have time to be processed by your body before you produce milk for the next feeding, minimizing the amount available to pass along to your child.

In addition, it will be important that your thyroid hormone levels and those of your baby are monitored regularly during the time you breastfeed.

12 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Mary Shomon
Mary Shomon is a writer and hormonal health and thyroid advocate. She is the author of "The Thyroid Diet Revolution."