Hyperthyroidism, or overactive thyroid, occurs when the thyroid gland produces too much hormone. This can have effects throughout the body, including diarrhea, difficulty breathing, and fatigue.

The thyroid is a butterfly-shaped gland in the neck. The hormones it produces and releases into the bloodstream control the body’s growth and metabolism.

Around 1 in 100 people over the age of 12 years in the United States have hyperthyroidism. It is most likely to occur in individuals over 60 years.

Hyperthyroidism is separate from hypothyroidism, or underactive thyroid. “Hyper” means there is too much thyroid hormone in the system, while “hypo” means there is not enough.

Without treatment, hyperthyroidism can lead to severe complications. However, medication can normally control it by reducing thyroid hormone production.

This article provides an overview of hyperthyroidism, including its causes, symptoms, diagnosis, complications, and treatments.

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Hyperthyroidism occurs when the thyroid gland produces too much thyroxine and triiodothyronine, two types of hormones.

If symptoms arise, they can affect the whole body and many body functions. Excessive thyroid hormones cause an increase in metabolism, which accounts for most symptoms.

These symptoms vary between individuals and can include:

  • a goiter, a swelling in the neck due to an enlarged thyroid gland
  • nervousness, irritability, mood swings, and reduced concentration
  • diarrhea
  • difficulty breathing
  • fatigue and difficulty sleeping
  • muscle weakness
  • hyperactivity
  • oversensitivity to heat, excessive sweating, and warm, damp skin
  • increased appetite
  • increased bowel movements and urination
  • infertility and a loss of interest in sex
  • itchy skin with raised, itchy swellings, called hives or urticaria
  • nails becoming loose
  • menstrual problems, especially lighter periods or absence of periods
  • alopecia, or patchy hair loss
  • a faster heartbeat, sometimes with palpitations
  • redness on the palms of hands
  • sudden weight loss
  • trembling hands and shakiness

Some medications treat the symptoms of hyperthyroidism, such as heart problems, while others aim to address the production of thyroid hormone.

Beta-blockers

Beta-blockers cannot treat hyperthyroidism, but they can reduce the symptoms until other treatments take effect. However, this may take a few weeks or months.

Antithyroid drugs

Antithyroid drugs stop the thyroid gland from producing too much thyroid hormone. One common drug that doctors recommend is methimazole.

However, if a person is pregnant, a doctor may recommend the drug propylthiouracil instead during their first trimester, as methimazole may have negative effects on the fetus. Pregnant people may switch to methimazole later in the pregnancy.

According to the American Thyroid Association, about 20–30% of people living with Graves’ disease experience symptom remission when receiving treatment for a period of 12–18 months with antithyroid drugs.

Adverse effects of medications can include:

  • allergic reactions
  • reduced white blood cells, increasing the chance of infections
  • liver failure, in rare cases

Radioactive iodine

Radioactive iodine enters active thyroid cells and destroys them. The destruction is local, and there are no widespread side effects. The dose of radioactivity within the radioiodine is very low and is not harmful.

However, radioiodine treatment is not suitable for pregnant or breastfeeding individuals. Doctors recommend avoiding pregnancy for 6–12 months after treatment.

Surgery

Surgery can remove part or all of the thyroid gland if other treatments are not viable. A surgical approach might be more suited for people who are pregnant, those who cannot tolerate other therapies, or those living with cancer.

Read more about thyroid gland removal.

There are various possible causes of hyperthyroidism, including the below.

Graves’ disease

Graves’ disease is an autoimmune condition and the most common cause of hyperthyroidism, accounting for over 70% of cases.

It is unclear what triggers Graves’ disease, but it often runs in families, suggesting a genetic basis.

The condition is most common in people aged 30–50 years and is seven to eight times more likely in females compared with males.

The condition can affect the eyes, causing protracted eyelids, bulging eyes, double vision, and swelling around the eyes.

Nodular thyroid disease

Thyroid nodules are lumps that develop in the thyroid gland. It is unclear why they occur.

These lumps may contain abnormal thyroid tissue, but they are usually benign or noncancerous. They affect the regular function of the thyroid, causing overactive thyroid.

The thyroid may become enlarged, and while people usually do not experience pain, they may be able to feel the nodules with their fingertips.

Excessive iodine intake

The thyroid gland removes iodine from the blood. Iodine comes from certain foods, such as seafood, bread, and salt. The thyroid gland uses the iodine to produce thyroid hormones.

Taking additional iodine in supplements can cause the thyroid gland to produce too many of the hormones.

People who take thyroid hormones as medication should follow up regularly with their doctor to make sure they are taking the right doses.

Medications

Some medications that treat heart problems contain a large amount of iodine, which may trigger changes in thyroid function. One drug that can affect thyroid function in this way is amiodarone, a drug doctors use to treat an irregular heartbeat.

Thyroiditis

Thyroiditis, an inflammation of the thyroid, often results from a viral infection. Symptoms include:

  • fatigue
  • sore throat
  • painful swallowing
  • generalized aches
  • neck pain

Hyperthyroidism occurs when the thyroid is overactive and produces too many hormones. By contrast, hypothyroidism develops when the thyroid does not produce enough hormones.

The two conditions share some common causes, such as thyroiditis, iodine intake, certain autoimmune disorders, or taking certain medications. However, hypothyroidism may also result from:

Symptoms of hypothyroidism can vary and are not specific to the thyroid. Some common symptoms that differ from hyperthyroidism include:

  • feeling cold quickly
  • tiring more easily
  • reduced mood
  • constipation
  • drier skin
  • forgetfulness

Diagnosing hypothyroidism often involves a physical examination, a complete family history, blood tests, and hormone tests. If a person receives a diagnosis, treatment will aim to manage the thyroid with thyroxine replacement.

There is no special diet that can resolve a thyroid disorder.

However, reducing the intake of excessive iodine in the diet and avoiding iodine supplements can help reduce imbalances in thyroid activity.

A balanced diet can help preserve thyroid health. If a person chooses to take supplements, they should ask a doctor for advice on how much to take and which supplements will not affect thyroid activity. Dietary changes that a person can try include:

  • adding dairy or nondairy alternatives
  • eating at least 5 servings of fruits and vegetables daily
  • drinking plenty of fluids, such as water, each day
  • eating foods high in fiber, including whole grains, potatoes, rice, and pasta
  • using unsaturated fats in cooking
  • choosing low fat proteins, such as chicken, beans, legumes, fish, and other sources

People may also find it useful to avoid foods and other products high in iodine, such as seaweed, certain cough medicines, and multivitamins. Additionally, a person can speak with their doctor about alternatives that may work better for them.

Read more about foods for hyperthyroidism.

The severity of hyperthyroidism and its symptoms depend on how well the body is able to react to the changes resulting from the excess thyroid hormones and how closely a person follows their treatment plan. Below is a list of possible complications from the condition.

Graves’ ophthalmopathy

Graves’ ophthalmopathy can cause pain or discomfort in the eye, light sensitivity, and certain vision problems. Additionally, a person’s eyes may protrude.

Using eye drops and wearing sunglasses can help relieve symptoms.

In severe cases, certain drugs, such as steroids or immunosuppressive drugs, can decrease the swelling behind the eyes.

A thyroid storm

A thyroid storm is an uncommon reaction that can occur after an infection, injury, or physical trauma, such as surgery or childbirth. It can also occur in pregnancy if the person has undiagnosed hyperthyroidism or difficulties in controlling the condition.

This is a life threatening reaction that requires emergency medical treatment.

Signs and symptoms indicating a thyroid storm include:

To diagnose hyperthyroidism, a doctor will ask about a person’s symptoms, perform a physical exam, and order blood tests.

Diagnosing advanced hyperthyroidism is normally straightforward because the signs are clear, but in the early stages, they are less obvious.

A blood test, known as a thyroid function test, can show how well the thyroid gland is working. The test checks for levels of thyroid stimulating hormone (TSH), thyroxine, and triiodothyronine.

Learn more about the TSH test.

Healthcare professionals may also carry out a special diagnostic scan of the thyroid gland using radioactive iodine to gauge thyroid function. This is known as a radioactive iodine uptake test.

People with hyperthyroidism may have more difficulty becoming pregnant.

Thyroid hormone levels rise slightly during pregnancy. Some individuals who are susceptible but have not received a diagnosis may have a slightly hyperactive thyroid during pregnancy.

Those with overactive thyroid may find that their thyroid enlarges slightly during pregnancy.

Severe, untreated hyperthyroidism during pregnancy may have links to:

However, with appropriate treatment, most pregnancies progress without issues.

Hyperthyroidism, or overactive thyroid, is more common among females. It has various causes, the most common being Graves’ disease.

People can treat hyperthyroidism and manage its symptoms using various medications, while some dietary changes may also help.