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Breastfeeding and Thyroid Disease, Questions and Answers
Can You Nurse Your Baby When Hypothyroid, Taking Thyroid Drugs Like Synthroid, or With Hyperthyroidism or Graves' Disease and Taking Antithyroid Drugs Like Tapazole or PTU

by Mary Shomon

Can I breastfeed if I'm hypothyroid?

Yes. There's no reason why a woman who is hypothyroid and on thyroid hormone replacement shouldn't or can't breastfeed under normal circumstances.

Should I continue taking my thyroid hormone drugs (i.e., Synthroid, Levoxyl, Armour, Thyrolar) when I'm breastfeeding?

Yes. Thyroid hormone replacement, when provided in proper dosage level, crosses into breast milk in only minute quantities, and has no adverse effect on the baby.

That said, this holds true only if the blood hormone levels remain in the normal range. If too much thyroid hormone is being taken and levels become hyperthyroid, then thyroid hormone can pass into the breastmilk. For this reason, if you are a nursing mother on thyroid hormone, you must take medication exactly as prescribed by a physician. The period following delivery is one where thyroid levels can fluctuate, so frequent testing is very important, because your dosage and TSH level may be just right three months post-partum, but three months later, the same dosage could be making you hyperthyroid. So, plan to get blood levels drawn frequently (i.e., every three months) as long as you are nursing your baby.

Stopping your thyroid hormone, or taking less than prescribed, is also not recommended, because not only is that insufficient treatment for your hypothyroidism, and putting you at risk of various symptoms and side-effects of hypothyroidism, but proper thyroid hormone replacement is actually necessary for normal lactation. (

cover.jpg - 45036 BytesHyperthyroidism or having an overactive thyroid gland can pose special concerns during pregnancy. When the body delivers too much thyroid hormone, both the mother and the baby can suffer. Miscarriages, premature births, and intrauterine growth retardation can occur when the disorder goes undiagnosed or untreated. Pregnant women with hyperthyroidism can also develop high blood pressure, and are at greater risk of heart conditions.

Does hypothyroidism cause any breastfeeding problems?

The likelihood is, if you are hypothyroid, and taking the proper dose of thyroid hormone replacement, you will be able to nurse your baby. However, La Leche League's Breastfeeding Answer Book says, "Women with a history of thyroid problems may need to be retested if their nursing baby is slow in gaining weight, as changes in metabolism can affect milk production."

Some women who are hypothyroid, myself included, appear to have problems with milk supply. I my case, I was very much in favor of breastfeeding my daughter, and prior to her birth, I had read several books, gone to a La Leche meeting, had some advance training from my doula (birth attendant), and after Julia was born, had several sessions with the hospital's lactation consultant.

I felt thoroughly prepared to nurse my daughter, and after she was born, all the experts assured me that she had latched on fine and we were doing well. After a week, however, she hadn't had many wet or dirty diapers, and had lost weight. I was not becoming engorged in between nursings, and after more visits to the lactation consultants and doula, the theory was that I didn't have a sufficient enough milk supply, and Julia didn't have a very strong sucking reflex. After trying many methods of increasing milk supply recommended by the various resources I called on -- everything from herbs like fenugreek, a nursing vacation, and nursing every 2 hours -- Julia continued to lose weight. At the three-week point, the pediatrician insisted that I add supplemental formula for Julia. Julia immediate began gaining weight. At that point, I also turned to pumping to help increase my milk supply, and despite a program of pumping, nursing and using the supplemental nursing system, I was able to pump only about half the typical milk supply of other mothers at this post-partum stage. It was then clear that I had a low milk supply, and had probably had if from the beginning.

Suspecting my thyroid was out of whack, I was tested, and they discovered that I'd become very hyperthyroid, with a TSH level of less than .05. My dosage was readjusted to return me to the TSH 1 to 2 range, but this never resulted in a rebound in milk supply. It may have been too late to kickstart it. But my recommendation is new mothers might want to get TSH tested a few days after delivery, so dosage modifications can be made right away if needed. Despite the low milk supply, I did manage to successfully pump about half of Julia's needed milk until she was six months old, when my supply stopped. I am still proud of this accomplishment, given the challenges.

If my baby is found to be hypothyroid, can I take the thyroid hormone myself, and have it pass through into the breastmilk?

No. If your baby is found to be hypothyroid (the mandatory "heel stick" test conducted on all newborns in the U.S. tests for hypothyroidism), the infant will need thyroid treatment right away to normalize thyroid levels. Untreated hypothyroidism in newborns must be treated, or the child is at risk of developmental and growth delays and impairment. The amounts of thyroid hormone that pass into breast milk are not sufficient to act as a substitute for direct treatment for hypothyroidism in a newborn. (

Can I get a thyroid scan when I'm breastfeeding?

A thyroid scan is typically not recommended while breastfeeding. A thyroid scan involves an injection of radioactiove iodine, and that is not something that can be given to a nursing mother. The radioactive iodine will pass into the milk for weeks, and can concentrate in the baby's thyroid. So, if a doctor suggests a thyroid scan, you can ask the doctor whether an alternative diagnostic procedure -- for example, blood testing, or fine needle aspiration -- can be performed instead of the scan, or, you should ask the doctor if the test is necessary in the first place. The primary reason for a scan in a nursing mother is to determine whether you have postpartum thyroiditis (frequently, a temporary condition), versus Graves' Disease. If a scan needs absolutely needs to be done, it is possible to do a thyroid scan with technetium, rather than radioactive iodine, according to breastfeeding expert, Dr. Jack Newman. He says, "Technetium has a half life (the length of time it takes for half of all the drug to leave the body) of 6 hours, which means that after 5 half lives it will be gone from the mother's body. Thus, 30 hours after injection all of it will be gone and the mother can nurse her baby without concern about his getting radiation." (

Can I get Radioactive Iodine Treatment / RAI while I'm breastfeeding?

No. While the most popular treatment for Graves' Disease and hyperthyroidism in the U.S. is the treatment known as "radioactive iodine," or RAI, this treatment should be deferred in women who are breastfeeding. The radioactive iodine appears in the breast milk, and can pose a danger to the infant's thyroid. RAI is also frequently used as a treatment for thyroid cancer, following surgery. (

Can I breastfeed while taking antithyroid drugs like Methimazole, Tapazole, or PTU, as a treatment for hyperthyroidism / Graves' Disease?

Methimazole (Tapazole) may cause thyroid suppression and goiter in nursing infants. Most doctors would advise that this drug not be used, or if it were required, careful monitoring of the breastfeeding infant's thyroid function would be needed, at intervals of every three months, at minimum, while the mother is on antithyroid drugs. According to the RxList drug information database online, "postpartum patients receiving Tapazole should not nurse their babies." (

Whether or not a nursing mother with Graves' Disease or hyperthyroidism should take the antithyroid drug propylthiouracil (PTU) is controversial. Some doctors believe that PTU use by a nursing mother, with regular monitoring of the infant's thyroid function, is safe. They recommend careful monitoring of the breastfeeding infant's thyroid function every three months while the mother is on antithyroid drugs, but because low amounts of PTU cross into the milk, they feel that it is safe for the infant.

Breastfeeding educators believe that mothers should continue to breastfeed, believing that women should continue breastfeeding, have their babies regular monitored. Their argument is that the benefits of breastfeeding outweigh taking breast milk with a little PTU, as long as you can monitor the baby's levels.

A July, 2000 study in the journal Pediatrics, however, found that more than one-third of pediatricians and endocrinologists still advise against breastfeeding for those mothers taking PTU, despite some current journal research claiming it is safe. (Read abstract of "Choice of Breastfeeding and Physicians' Advice: A Cohort Study of Women Receiving Propylthiouracil," Pediatrics. Vol. 106 No. 1 July 2000, pp. 27-30.)

Despite studies showing the safety, some doctors are not convinced that breastfeeding should be encouraged in women taking antithyroid drugs. They cite concerns over potential nonthyroid side effects of antithyroid drugs, for example, autoimmune disturbances. For example, autoimmune disorders such as lupus and arthritis can be a rare but serious complication of antithyroid drugs.


  • Thyroid Guide to Pregnancy, Fertility & Breastfeeding Success -- Covers key information on undiagnosed and/or undertreated thyroid problems and their impact on the ability to become pregnant as well as miscarriage, and breastfeeding. The book also discusses thyroid conditions, including hypothyroidism, hyperthyroidism, Graves' disease, Hashimoto's disease, thyroid nodules, goiter, and thyroid cancer, and their impact on pregnancy.
  • Thyroid Disease and Pregnancy -- The range of issues related to fertility, pregnancy and their relationship to thyroid disease are explored, and helpful guidelines are provided on how to have a healthy pregnancy with thyroid disease.
  • La Leche League -- The nation's most prominent support group for nursing mothers, and advocates of breastfeeding.\
  • Promotion of Mother's Milk, Inc. -- Website, offering articles, message boards, and advice about breastfeeding.
  • Dr. Jack Newman's Breastfeeding Articles -- An excellent resource on all facets of breastfeeding

Sticking Out Our Necks and this website are Copyright Mary Shomon, 1997-2003. All rights reserved. Mary Shomon, Editor/Webmaster
All information is intended for your general knowledge only and is not a substitute for medical advice or treatment for specific medical conditions. You should seek prompt medical care for any specific health issues and consult your physician or health practitioner before starting a new treatment program. Please see our full disclaimer.