Hyperthyroidism is when the thyroid gland produces too much thyroid hormone. It has many causes, such as infection, pregnancy, and iodine overexposure. Several conditions can also cause hyperthyroidism.

The thyroid gland is a small organ within the neck. Its main function is to produce two thyroid hormone before releasing them into the bloodstream. These hormones are thyroxine (T4) and triiodothyronine (T3).

When someone has hyperthyroidism, their thyroid gland produces too much T4 and T3.

This article outlines some causes of hyperthyroidism. It also describes the diagnosis, treatment, and outlook of hyperthyroidism.

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According to a 2018 study, hyperthyroidism can arise for many different reasons. Some possible causes of hyperthyroidism include:

  • an overstimulated thyroid
  • an increase in the number of thyroid cells
  • damage to certain thyroid cells
  • exposure to certain medications

According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), consuming too much iodine may cause the thyroid to produce too much thyroid hormone, leading to hyperthyroidism. Some heart drugs, cough medications, and seaweed-based products may contain a lot of iodine.

Some people taking medication to treat hypothyroidism take too much, which raises their thyroid hormone levels. Anyone taking such medication should have a doctor check their hormone levels at least once a year. They should also discuss drug interactions with a doctor before taking any new medications.

Despite the many pathways to hyperthyroidism, some of its causes are more frequent than others. The most common causes of hyperthyroidism are:

  • Graves’ disease
  • toxic nodular goiter
  • thyroiditis

According to a recent review, Graves’ disease is the most common cause of hyperthyroidism. Graves’ disease mostly affects the thyroid gland, although it can also affect the skin and eyes.

Graves’ disease is an autoimmune disease. It arises when the immune system mistakes the body’s cells for foreign invaders and attacks them. Scientists do not know exactly how the process unfolds in Graves’ disease. However, there are several risk factors for this condition. They include:

  • being pregnant
  • stress
  • smoking
  • infections
  • iodine overexposure

People with a family history of Graves’ disease have an increased risk of developing the condition.

Learn more about Graves’ disease.

Goiter is an enlargement of the thyroid gland. As a 2022 article explains, there are several forms of goiter. Nodular goiter is one of them.

Toxic nodular goiter arises when small, round masses appear within an enlarged thyroid. These are nodules. In people with toxic nodular goiter, these nodules produce too much thyroid hormone.

There are several risk factors for goiter. The following are more commonly associated with diffuse goiter but may present with nodular goiter in some cases:

  • postpartum thyroiditis
  • autoimmune thyroiditis
  • radiation thyroiditis

Iodine deficiency can also cause goiter. As the same review explains, iodine deficiency is the most common worldwide cause of goiter. However, it is relatively rare in the United States.

Learn about multinodular goiter.

Scientists define thyroiditis as an inflamed thyroid gland. There are many causes of thyroiditis, including:

Not every form of thyroiditis causes hyperthyroidism. For example, Hashimoto thyroiditis causes hypothyroidism, which is when the thyroid produces too little T4 and T3.

The hormones T4 and T3 have a wide range of functions. For this reason, hyperthyroidism has a large number of possible symptoms. They include:

Depending on an individual’s symptoms, doctors can recommend further testing. The thyroid stimulating hormone (TSH) test is an important initial test for hyperthyroidism.

The TSH test is a blood test. After using a needle and syringe to take a blood sample, medical staff will measure its TSH levels. The body produces less TSH when someone has elevated thyroid hormone levels. Therefore, low blood TSH levels indicate hyperthyroidism.

Doctors will usually follow a TSH test with further blood tests. These might directly measure T4 or T3 levels. After making a hyperthyroidism diagnosis, doctors will then try to discover its underlying cause.

Most hyperthyroidism cases arise from Graves’ disease or toxic nodular goiter. For this reason, doctors need to test for these conditions. This testing might involve looking closely at symptom history and feeling the thyroid.

Learn more about the TSH test.

There are many ways of treating hyperthyroidism. Scientists have discovered several drugs that can help to manage the symptoms. These include atenolol (Tenormin) and verapamil (Verelan/Calan).

There are also different methods of treating the underlying cause of hyperthyroidism. They include:

  • radioactive iodine therapy
  • thionamide therapy
  • subtotal thyroidectomy

Different causes of hyperthyroidism warrant different treatments. For example, radioactive iodine therapy is especially helpful for Graves’ disease.

Learn about foods to eat and avoid with hyperthyroidism.

Anyone with symptoms of hyperthyroidism should seek medical advice. This is especially true if an individual belongs to an at-risk group for thyroiditis, goiter, or Graves’ disease. An earlier diagnosis could make treatment more effective.

A 2022 article suggests that the outlook for people with hyperthyroidism tends to be positive if they receive treatment. Medications are highly effective in helping to manage symptoms.

If someone does not receive treatment for hyperthyroidism, this can cause a condition called thyroid storm. This is an extreme form of hyperthyroidism, which can be life threatening. Scientists believe that the mortality rate for thyroid storm might be 8–25%.

Learn more about thyroid storm.

There are several causes of hyperthyroidism, with Graves’ disease and toxic nodular goiter being the most common.

Someone with hyperthyroidism may experience symptoms such as fatigue, nervousness, and shortness of breath.

Doctors may recommend a TSH test if they suspect an issue with the thyroid. Low low levels of TSH indicate hyperthyroidism.

Although potentially serious, medications are effective at treating the condition. Depending on the root cause of hyperthyroidism, doctors may recommend other therapies or surgery.