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Breastfeeding and thyroid disease

The thyroid gland

The main function of the thyroid gland is to make thyroxine (T4) and triiodothyronine (T3) hormones. These hormones are important for the growth and normal function of the body, as well as for breastfeeding.

Thyroid disease

Thyroid diseases include hypothyroidism (under-active thyroid), hyperthyroidism (over-active thyroid), and thyroid cancer. There is also a condition called post-partum thyroiditis which sometimes includes both a hyperthyroid phase and a hypothyroid phase.


Symptoms of hypothyroidism include:

  • fatigue

  • weight gain

  • intolerance to cold

  • low mood

  • heavy and prolonged menstrual flow

  • absence of a menstrual period in a woman of reproductive age

  • constipation

  • dry scaly skin

  • hair loss.

Some breastfeeding mothers with hypothyroidism struggle to make a full milk supply. Thyroid hormones play a role in normal breast development and helping breasts to make milk. When not enough of the thyroid hormones are made, a mother’s milk supply may be affected.

Hypothyroidism is treated with thyroxine in order to bring the levels back to normal. Women who have been properly treated for hypothyroidism report they have had no problems with their milk supply.

Some women report that their milk supply is sensitive to the level of thyroid hormone in their bloodstream. That is, some women report that having their thyroid hormone levels within the normal range was not enough to support full milk production but they have a full milk supply when their thyroid hormone level is within the upper part of the normal range. This may reflect their own personal set point. 


Symptoms of hyperthyroidism include:

  • fatigue

  • tremors

  • anxiety

  • palpitations

  • intolerance of heat

  • sweating

  • weight loss

  • increased pulse rate

  • diarrhoea

  • light or no menstrual flow.

Hyperthyroidism is usually treated with anti-thyroid drugs which reduce the amount of thyroid hormones being made. Radioactive iodine or surgery are other treatments for hyperthyroidism, particularly if it is long standing or difficult to control with medication.

In the 12 months after a woman gives birth, it is important that hyperthyroidism due to Graves’ disease is not confused with the hyperthyroid phase of post-partum thyroiditis (see below). This is important since these two conditions have different causes and treatments.

Some women with hyperthyroidism report a large milk supply, but others seem to have difficulty with their let down reflex.

Post-partum thyroiditis

Post-partum thyroiditis is an autoimmune disease which can occur during the first year after a woman has given birth. During pregnancy, the immune system is naturally suppressed so that it doesn’t attack the developing foetus. After birth, the mother’s immune system becomes heightened once again. This ‘immune rebound’ can trigger post-partum thyroiditis. Post-partum thyroiditis may represent a thyroid autoimmunity that was silent before pregnancy. 

Post-partum thyroiditis may present as hypothyroidism alone, hyperthyroidism alone, or hyperthyroidism followed by hypothyroidism.

Many symptoms of hypothyroidism or hyperthyroidism are common in the post-partum period in ‘normal’ women so the diagnosis can be missed or not considered by the woman or her medical adviser. Also, some thyroid problems may be mistaken as postnatal depression or other illnesses.

Most women recover from post-partum thyroiditis. However, a small percentage remain hypothyroid, and many more are at risk of developing thyroid disease later in life. Some women with post-partum thyroiditis report milk supply problems, others breastfeed without difficulty.

Thyroid cancer

Thyroid cancer carries risks to the breastfeeding mother and her baby in both diagnosis and treatment, as both require the use of radioactive drugs including radioactive iodine which preclude breastfeeding.

Thyroid disease medication and breastfeeding

Women who have thyroid disease prior to becoming pregnant need to have their thyroid levels checked often throughout pregnancy and while breastfeeding. It is often necessary to adjust medication doses to maintain normal thyroid hormone levels.

Few medications are contraindicated when breastfeeding. Many breastfeeding mothers with thyroid disease take medications to treat it and safely continue to breastfeed. For accurate and up-to-date information about the use of medications and breastfeeding, contact one of the telephone numbers listed on the website article Breastfeeding and prescription medications.


Speller, E., Brodribb, W 2012, Breastfeeding and Thyroid disease: A literature review, Breastfeeding Review 20(2),41-47.

The information on this website does not replace advice from your health care providers.

© Australian Breastfeeding Association August 2017



Last reviewed: 
Aug 2017