Thyroid-stimulating hormone (TSH)

Thyroid-stimulating hormone, a blood test that checks whether the thyroid gland is working normally.

What TSH is

TSH is a hormone released by the pituitary gland in the brain. Its job is to tell the thyroid gland in the neck how much thyroid hormone to make. The thyroid in turn controls metabolism, the rate at which the body uses energy. When the thyroid makes too little, the pituitary usually raises TSH to stimulate it. When the thyroid makes too much, TSH usually falls. Because of this relationship, a TSH blood test is a useful and common way to check whether the thyroid gland is working normally.

How it relates to PCOS

Thyroid problems such as an underactive thyroid can cause irregular periods, weight changes, fatigue, and mood changes. These signs overlap with PCOS, so the two conditions can sometimes be confused or exist together. That is why guidelines recommend a TSH test to rule out a thyroid cause before PCOS is confirmed. This step helps make sure the real cause of symptoms is identified and treated correctly. See PCOS symptoms and what is PCOS to understand this overlap more clearly.

How a result is interpreted

In general, a high TSH points to an underactive thyroid, while a low TSH points to an overactive one. However, the result is always interpreted by a doctor alongside symptoms and other thyroid tests, not as a single number. Reference ranges can also differ between laboratories and with conditions such as pregnancy. TSH is not a measure of how severe PCOS is, and one value alone does not tell the whole story. Thyroid hormones are different from the sex hormones usually discussed in PCOS.

What it means for you

If a doctor orders a TSH test, it is usually part of a wider assessment to understand the cause of your symptoms. If the result falls outside the usual range, a doctor may suggest a follow-up test or a referral to a specialist. If you have already had a test and are unsure what it means, bring the result to your appointment. Any decision about testing, medicine, or treatment should be made with a doctor.

This glossary is education, not diagnosis. For your own situation, ask a doctor or pharmacist.