Breastfeeding and thyroid disease

If you have a thyroid condition (or have just been diagnosed) and you’re breastfeeding or planning to breastfeed, you might be wondering how your health could affect feeding your baby. 

This article provides information about breastfeeding, milk supply, medication safety, and where to get further help.

The thyroid gland sits at the front of your neck and makes hormones that help your body work well. These hormones also play an important role in breastfeeding, supporting breast development and milk production. If your thyroid isn’t working as it should, it can sometimes affect how much milk you make or how you feel while breastfeeding.

Diseases of the thyroid include hypothyroidism (under-active thyroid), hyperthyroidism (over-active thyroid), post-partum thyroid disfunction and thyroid cancer.  

If you have hypothyroidism, your thyroid isn’t making enough hormones. Because hormones are needed for milk production, mums with hypothyroidism find it harder to make a full milk supply, especially if their thyroid levels aren’t well managed. 

If you find you’re struggling with low milk supply, despite frequent feeding, talk to your doctor. Your thyroid medication may need adjusting. Many mums find that once their thyroid levels are in the right range, breastfeeding becomes easier.

Hyperthyroidism means your thyroid is making too many hormones. This can sometimes cause a larger milk supply, but some mums find it affects their let-down reflex (milk flow). Treatment for hyperthyroidism includes anti-thyroid medication, radioactive iodine, or surgery. These are usually safe for breastfeeding but always check with your doctor about your specific medicines. 

If you notice changes in your milk supply or how breastfeeding feels, let your healthcare provider know. They can help you manage both your thyroid health and breastfeeding.

Postpartum thyroiditis is a thyroid condition that can develop in the first year after having your baby. It can cause your thyroid to be overactive, underactive, or even switch between the two. Some mums with postpartum thyroiditis notice changes in their milk supply, but many can breastfeed without any problems. 

Symptoms can be similar to normal post-birth changes or even postnatal depression. It’s important to talk to your doctor if you feel unwell or notice changes in your breastfeeding experience. 

Most mums recover from postpartum thyroiditis, but some may need ongoing thyroid care.

Thyroid cancer carries risks to the breastfeeding mother and her baby in both diagnosis and treatment. Both require the use of radioactive drugs including radioactive iodine which means you can't breastfeed.  

If you had a thyroid condition before pregnancy, your doctor will usually check your thyroid levels regularly during pregnancy and while you’re breastfeeding. Your medication dose might need to change to keep your hormone levels in the right range.

Almost all thyroid medicines are safe to take while breastfeeding. Many mums continue their thyroid treatment and breastfeed without any problems. If you’re unsure about your medication, or if your dose changes, check with your doctor or pharmacist. 

Breastfeeding and medicines

Australian Thyroid Foundation (ATF)

National patient authority for thyroid health, education, and advocacy.

Provides clear information on thyroid conditions, symptoms, diagnosis, and management.

Website: Australian Thyroid Foundation

Thyroid Australia

Offers reliable, easy-to-understand information for patients and families.

Website: Thyroid Australia

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

© Australian Breastfeeding Association June 2026