A variety of hormones control the menstrual cycle. This network of hormones impacts thyroid function, although the relationship between menstruation, reproductive function, and the thyroid is complex.

People with hyperthyroidism, an overactive thyroid, and hypothyroidism, an underactive thyroid, may be at higher risk of disturbances and irregularities in their menstrual cycles.

This article looks at how hyperthyroidism can affect the menstrual cycle, other symptoms, and more.

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Hyperthyroidism is when the thyroid gland, a small, butterfly-shaped gland at the front of the neck, produces more thyroid hormones than the body needs.

Thyroid hormones are essential to most bodily functions, systems, and organs, including the menstrual cycle and reproductive system.

In people with hyperthyroidism, menstruation may occur irregularly, and menstrual flow may be lighter. This may cause fertility problems.

Hyperthyroidism can cause low levels of a protein called sex hormone binding globulin (SHBG). This protein attaches itself to both male and female sex hormones.

A person with abnormal SHBG levels may experience fertility problems.

Learn more about infertility here.

Hyperthyroidism can cause various menstruation problems, including:

Irregular periods

According to some experts, an irregular period is when there are less than 24 days or more than 38 days between periods.

However, other organizations have different criteria. For example, a 2021 review indicated that some research classifies an irregular period as less than 21 days or longer than 35 days.

Other information suggests that a period is also irregular if the length of the menstrual cycle varies by more than 20 days month-to-month.

An irregular menstrual cycle is a potential complication of hyperthyroidism.

Learn more about irregular periods here.

Lighter or fewer periods

People with hyperthyroidism are more likely to experience abnormally low bleeding during periods. This is known as hypomenorrhea.

Hyperthyroidism can also cause a person to have fewer periods.

Learn more about lighter periods here.

Stopped periods

The absence of periods is called amenorrhea.

In thyroid disorders, such as hyperthyroidism, elevated levels of the hormone prolactin in the blood may lead to impaired ovulation, which can cause irregularities and stoppages in menstruation.

This can cause fertility problems.

Learn more about the absence of periods here.

Fertility problems

Because hyperthyroidism can affect ovulation, which is the release of an egg from the ovary, it can affect fertility.

Increased prolactin levels can prevent the egg, or ovum, from releasing and traveling down the fallopian tube in preparation for fertilization.

This can make it more difficult for a person to become pregnant.

Learn more about infertility here.

Early menopause

If the immune system is the cause of a person’s hyperthyroidism — for example, in Graves’ disease — it may affect other glands, including the ovaries.

When this occurs, the condition can lead to premature menopause before the age of 40.

Learn more about the signs and symptoms of menopause here.

Other conditions or factors can influence a person’s menstrual cycle.

Irregular, heavy, or very painful periods can indicate other health problems, such as endometriosis, polycystic ovary syndrome (PCOS), or uterine fibroids.

Typically, irregular periods only occur if a person is:

Other potential causes of irregular periods include:

Learn more about other causes of menstrual changes.

A person may be unable to prevent issues with their menstrual cycle without treating the underlying hyperthyroidism.

Taking the appropriate medications for hyperthyroidism will help a person prevent abnormally light or irregular periods.

An excess of iodine can cause or worsen hyperthyroidism. In people with Graves’ disease or other autoimmune disorders, excessive iodine may cause harmful side effects.

People can discuss limiting or avoiding sources of iodine with their doctor to reduce symptoms. These may include:

  • iodine supplements
  • foods that contain iodine, such as kelp and iodized table salt
  • certain multivitamins and cough syrups

Stopping smoking may also help prevent hyperthyroidism.

Learn more about the best foods for hyperthyroidism.

Talking with a doctor about any symptoms of hyperthyroidism is important, as an overactive thyroid can lead to serious medical issues if left untreated.

As well as menstrual irregularities, symptoms include:

Learn about other thyroid disorders here.

Doctors can treat menstrual cycle issues due to hyperthyroidism by addressing the underlying condition.

Doctors can treat hyperthyroidism with medication, surgery, and radioiodine therapy.

After successful treatment, a person’s periods and ovulation may return to their usual cycle pattern.

The long-term outlook of the condition depends on various factors, including the cause of hyperthyroidism and a person’s general health.

If left untreated, hyperthyroidism can lead to severe health problems.

These include:

Learn about TSH hormones and testing for levels here.

This section answers some frequently asked questions about hyperthyroidism and the menstrual cycle.

Why does hyperthyroidism cause menstrual problems?

Hyperthyroidism can cause menstrual problems because it leads to:

  • higher production of the protein sex hormone-binding globulin (SHBG), which can lead to irregular, lighter, or missed periods
  • elevated levels of the hormone prolactin in the blood, which can affect menstruation, ovulation, and fertility

Can I get pregnant with hyperthyroidism?

A person with hyperthyroidism can get pregnant, but the condition may make it significantly more difficult to conceive.

This is because hyperthyroidism can impair ovulation and prevent the ovum from descending the fallopian tube where sperm may fertilize them.

A person may wish to contact a doctor if they have hyperthyroidism and wish to become pregnant. A doctor may recommend fertility treatments and treatments for hyperthyroidism.

Hyperthyroidism in pregnancy carries risks to the parent and baby, so a doctor will need to closely monitor any pregnancy.

Do you ovulate with hyperthyroidism?

Hyperthyroidism can prevent a person from ovulating, as it can elevate prolactin levels and affect SHBG in the body. This interferes with the ovaries, preventing eggs from traveling down the fallopian tube ready for fertilization.

However, this is not always the case, and a person with hyperthyroidism may still ovulate.

People with hyperthyroidism often have higher levels of the hormone prolactin in their bodies than usual.

High levels of prolactin and the protein SHBG can interfere with the functioning of the ovaries, causing periods to become irregular, infrequent, or lighter than usual. It can also cause periods to stop.

Because hyperthyroidism may directly affect ovulation, it can lead to infertility or difficulty conceiving.

If a person does not receive treatment, hyperthyroidism can lead to serious health problems.

A person with symptoms of hyperthyroidism should contact a doctor. Treatment can involve medication, such as beta-blockers, antithyroid medication, surgery, and radioiodine therapy.

Following treatment, a person’s menstrual cycle should return to normal.