Hypothyroidism doesn’t cause polycystic ovary syndrome (PCOS), but having PCOS may increase your risk of thyroid dysfunction.

PCOS and hypothyroidism both affect the endocrine system, which produces hormones.

Both have similar symptoms, such as weight gain and irregular menstrual cycles, which can make diagnosis difficult. However, PCOS can only be diagnosed when other conditions have been ruled out.

Generally, doctors will rule out thyroid disorders like hypothyroidism before diagnosing PCOS.

Research suggests that people with PCOS are more likely to have a thyroid disorder. Hypothyroidism is commonly seen in people with PCOS.

Why is still unclear. Researchers have proposed things like genetic factors and altered hormone levels.

There is no evidence to suggest that having hypothyroidism means you’re more likely to develop PCOS.

While the size of ovaries and ovarian cysts have been noted in people with hypothyroidism, that doesn’t mean it leads to PCOS down the line.

Experts still aren’t sure what causes PCOS. But some factors that may increase the risk of developing it include having:

  • a family history of PCOS
  • type 2 diabetes
  • overweight or obesity
  • androgen level imbalances

While there’s no evidence that hypothyroidism increases the risk of PCOS, there is a possibility that PCOS makes a person more likely to develop thyroid conditions.

Research suggests that people with PCOS have higher rates of autoimmune thyroid disorders such as Graves’ disease and Hashimoto thyroiditis.

A 2019 Danish study found that people with PCOS had a 2.5 times higher risk of thyroid disease.

A 2018 analysis of six studies found that subclinical hypothyroidism (SCH) — which is a milder form of hypothyroidism that may be seen earlier on — was more common in people with PCOS.

Although a 2023 study did not find an association between SCH and PCOS, it’s generally accepted that the risk of SCH and hypothyroidism is higher in a person who has PCOS.

More research is needed to understand why. There are several possibilities:

  • an increase in body mass index and insulin resistance, which is seen with both conditions
  • hormonal imbalances, such as higher levels of androgens
  • genetic factors that are yet to be determined

Other things can affect the chance of being diagnosed with hypothyroidism.

Hypothyroidism is more common in people over age 50 and people assigned female at birth.

It can also be caused by viral or respiratory infections, birth defects, treatments or surgeries on or near the thyroid gland, and medications like lithium.

If you have PCOS, undergo regular thyroid screening.

Many symptoms of hypothyroidism and PCOS are similar, meaning one condition may be left undiagnosed and symptoms may worsen.

This can be an even bigger concern for fertility, as both conditions can make it more difficult to become pregnant.

Testing for hypothyroidism and other thyroid conditions is relatively straightforward. You’ll usually undergo a blood test to check levels of various thyroid hormones and whether they’re in the expected ranges.

If needed, scans may be used to check for abnormalities in the thyroid gland.

If you have both PCOS and hypothyroidism, it’s important to be aware that your symptoms may be more severe than people who only have one condition.

Thyroid conditions can worsen fertility symptoms, making it difficult to become pregnant. There’s also an increased risk of diabetes.

To manage these symptoms, you’ll likely be given medication to help regulate your thyroid hormone levels.

Anti-androgen medications may be needed to rebalance hormone levels affected by PCOS, while a drug called metformin can improve insulin levels.

Oral contraceptives are another option for PCOS treatment, but they aren’t suitable for people trying to get pregnant.

Other options include lifestyle changes, like exercise and diet alterations, and surgery to remove the thyroid gland in severe cases.

While there’s no evidence to suggest that hypothyroidism increases the risk of PCOS, there is an association between PCOS and subsequent hypothyroidism.

More research is needed to determine why. The symptoms of both issues can be similar, so it can be difficult to make a diagnosis.

If you have PCOS, your healthcare professional should regularly check your thyroid levels to make sure various hormones aren’t too high or too low.

Lauren Sharkey is a U.K.-based journalist and author specializing in women’s issues. When she isn’t trying to discover a way to banish migraines, she can be found uncovering the answers to your lurking health questions. She has also written a book profiling young female activists across the globe and is currently building a community of such resisters. Catch her on Twitter.