Introduction

The thyroid gland is one of the endocrine (hormone) glands in the body. These glands make hormones to regulate many different functions in the body. If the thyroid gland is overactive, it produces too much of the thyroid hormones. The medical term for an overactive thyroid is hyperthyroidism. It is most commonly caused by a condition known as Graves' disease.

The higher levels of thyroid hormones unnecessarily speed up a lot of functions in the body. This can lead to noticeable symptoms such as weight loss, sweating, nervousness or a rapid heartbeat. An overactive thyroid increases the risk of cardiovascular disease (problems affecting the heart and/or blood vessels).

If the thyroid gland doesn’t produce enough hormones, the body’s functions slow down. This problem is known as an underactive thyroid or hypothyroidism.

At a glance

• An overactive thyroid occurs if the thyroid gland makes too many hormones.
• This can lead to various problems, including nervousness, weight loss, a rapid heartbeat and an enlarged thyroid gland.
• An overactive thyroid is usually treated with tablets.
• If that doesn't help enough, surgery or treatment with radioactive iodine are considered.

Symptoms

Hyperthyroidism often causes the thyroid gland, which is located at the front of the neck, to become noticeably larger. A swollen thyroid is called a goiter. The whole gland isn’t always swollen. A lump (nodule) may be felt or seen instead. But some people have an overactive thyroid without a goiter or thyroid nodules – and those who have a goiter or nodules don’t always have an overactive thyroid.

The thyroid gland makes too many hormones

An overactive thyroid gland can cause many different symptoms

If there are too many thyroid hormones in your blood, various chemical reactions and functions in the body get out of balance. This can cause symptoms such as

• a pounding heart (palpitations) and rapid heartbeat, and sometimes an irregular heartbeat too,
• high blood pressure,
• weight loss despite an increased appetite,
• diarrhea,
• trembling, nervous restlessness, irritability, sleep problems and
• weakness and tiredness.

People who have an overactive thyroid often sweat a lot and feel uncomfortable when they are warm. Their skin is often warm and moist to the touch, and they may have thinning hair.

If the overactive thyroid is caused by Graves' disease, the eyes may be affected too.

Causes

The most common cause of an overactive thyroid gland is Graves’ disease. In this condition, a problem with the immune system causes the thyroid gland to make more thyroid hormones than normal.

Hyperthyroidism may also arise if thyroid gland cells start producing hormones “autonomously” – in other words, without being "told" to. The activity of the thyroid gland is usually regulated by the pituitary gland. Sometimes, though, the thyroid gland cells no longer react to signals from the pituitary gland. As a result, the thyroid gland may produce far more hormones than are actually needed. The autonomous cells are sometimes found in the whole thyroid gland, and sometimes they are only found in one or several benign (non-cancerous) growths called nodules. These growths are also known as "hot" nodules. High thyroid hormone levels are only very rarely caused by malignant (cancerous) thyroid tumors.

Sometimes too many thyroid hormones get into the blood if the thyroid gland is inflamed. Thyroid hormones that are stored in the inflamed tissue are then released, temporarily leading to symptoms similar to those caused by an overactive thyroid.

Prevalence

About 1 out of 100 people have an overactive thyroid, making it quite a common condition. It is more common in women than in men, and usually develops in middle age.

Effects

If people who have an overactive thyroid don’t get proper treatment, they may develop cardiovascular diseases such as atrial fibrillation (an irregular heartbeat). Because their old bone tissue is broken down and new bone tissue is formed at a faster rate, osteoporosis may develop over the long term too.

In rare cases, an overactive thyroid leads to a potentially life-threatening situation known as a thyrotoxic crisis or a “thyroid storm.” This can be triggered by iodine-containing medication or an x-ray contrast medium (a dye-like substance), for example. As well as the typical symptoms of an overactive thyroid, it can cause a high fever, vomiting, restlessness and anxiety, an irregular heartbeat, confusion and drowsiness, and sometimes even a coma or cardiovascular collapse (where not enough blood flows around the body). A thyroid storm is a medical emergency, requiring hospital treatment in an intensive care unit.

Diagnosis

If it is thought that you may have an overactive thyroid, the doctor will first ask you a few questions and then feel your thyroid gland from the outside by touching your neck. This allows them to see whether the gland is bigger than usual or has any nodules in it.

Blood tests can provide important information about the cause, including whether the excessive production of thyroid hormones is due to a problem with the thyroid gland itself or whether it is being caused by a problem with the pituitary gland. Signs of Graves' disease can also be detected in a blood test.

Ultrasound examinations allow doctors to take a closer look at the thyroid gland tissue and any nodules in the gland. An examination known as a thyroid scan (or thyroid scintigraphy) can be done to see whether a nodule is producing too many hormones (a "hot" nodule) or whether it is inactive (a "cold" nodule).

Treatment

Mild hyperthyroidism sometimes gets better on its own, without treatment. But the overproduction of thyroid hormones is usually first stopped using tablets called anti-thyroid drugs. If the function of the thyroid gland doesn't return to normal after treatment with these tablets, the thyroid gland is surgically removed or treated with radioactive iodine. Known as radioiodine therapy, this involves swallowing radioactive iodine which is then absorbed by your thyroid gland, where it destroys overactive cells.

If the overactive thyroid is caused by an enlarged thyroid gland with “autonomous” cells, the thyroid gland that has been “slowed down” with anti-thyroid drugs is usually surgically removed. If surgery isn’t possible or the thyroid gland isn’t greatly enlarged, radioiodine therapy tends to be more suitable.

Further information

When people are ill or need medical advice, they usually go to see their family doctor first. Read about how to find the right doctor, how to prepare for the appointment and what to remember.

Sources

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• Deutsche Gesellschaft für Nuklearmedizin (DGN). Radioiodtherapie bei benignen Schilddrüsenerkrankungen (Version 5). DGN-Handlungsempfehlung (S1 Leitlinie). AWMF-Registernr.: 031-003. 2015.
• Jameson JL, Mandel SJ, Weetmann AP. Disorders of the Thyreoid Gland. In: D. L. Kaspers, S. L. Hauser, J. L. Jameson, Fauci AS, D. L. Longo, J. Loscalzo (Ed). Harrison's Principles of Internal Medicine. McGraw-Hill Education; 2015.
• Kahaly GJ, Bartalena L, Hegedüs L et al. 2018 European Thyroid Association Guideline for the Management of Graves’ Hyperthyroidism. Eur Thyroid J 2018; 7(4): 167-186. [PMC free article: PMC6140607] [PubMed: 30283735]
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