Hyperthyroidism is the medical term for an overactive thyroid. This means the thyroid gland produces too much thyroid hormone, which speeds up your metabolism and leads to a variety of worrisome symptoms.

An overactive thyroid impacts many involuntary functions of the body, including circulation, digestion, and temperature regulation. Thus, an overactive thyroid can cause rapid, irregular heartbeats, unintended weight loss, increased appetite, anxiety, and sleep problems.

The good news is that there are several effective treatments for hyperthyroidism, and most people are able to control the condition with medication or other measures.

Hyperthyroidism occurs when the thyroid gland produces too much thyroid hormone. The thyroid is the butterfly-shaped gland located at the front of the lower neck, near the top of the collarbone. The gland is tiny, but its role is significant. The thyroid produces two hormones, thyroxine (T4) and triiodothyronine (T3), which affect the performance of almost all of the body’s organs, from the heart to the digestive system.

In someone with hyperthyroidism, their metabolism will speed up, leading to weight loss, increased appetite, a faster heartbeat, and gastrointestinal (GI) issues.

Although there are several causes of hyperthyroidism, Graves’ disease, an autoimmune condition, is the most common one. In a person with Graves’ disease, the immune system mistakenly attacks the thyroid, causing the gland to produce too much thyroid hormone.

Other causes of hyperthyroidism include:

• Thyroiditis (thyroid inflammation) from viral infections or certain medications
• Overactive thyroid nodules (small lumps within the thyroid gland)
• Post-pregnancy thyroid inflammation
• Consuming a high-iodine diet, in rare cases

People with hyperthyroidism experience symptoms such as:

• Unintentional weight loss
• Irregular heartbeat
• Rapid heartbeat
• Heart palpitations
• Hand tremors
• Anxiety
• Trouble concentrating
• Muscle weakness, especially in the thighs and upper arms
• Excessive sweating
• Skin that feels clammy to the touch

Older adults may have different symptoms, such as irritability, fatigue, or sleep issues, which can be mistakenly seen as signs of depression or dementia. Lab tests are able to distinguish between depression and thyroid conditions.

People are at greater risk of hyperthyroidism if they:

• Are female

• Have a family history of hyperthyroidism, thyroid disease, or Graves’ disease

• Have other autoimmune diseases

• Have thyroid nodules

• Consume a high-iodine diet (including seaweed)

• Take medication that contains iodine

• Take too much thyroid hormone

• Were pregnant during the 6 months prior to diagnosis

Your medical history, a physical exam, and diagnostic tests are all used to diagnose hyperthyroidism.

You should discuss your medical history with a doctor, sharing information about symptoms such as unexplained weight loss, muscle weakness, and heart palpitations. Let your doctor know if you have a personal or family history of thyroid conditions. If you take medication that contains iodine or typically eat a high-iodine diet (including seaweed and fish), that is important for doctors to know.

During a physical exam, doctors will look for the following signs of hyperthyroidism:

• Increased heart rate

• High blood pressure, particularly systolic blood pressure

• An enlarged thyroid

• Hand tremors

• Bulging eyes or inflammation around the eyes

• Changes to the hair, skin, or fingernails

Hyperthyroidism is usually diagnosed after doctors see the results of simple blood tests. The tests look at the levels of thyroid hormones (T4 and T3) and thyroid stimulating hormone (TSH). Additionally, you may have other blood tests that check blood glucose and cholesterol levels to rule out other conditions. Doctors may also recommend specialized tests, such as a thyroid receptor antibody test (TRAb) or thyroid stimulating immunoglobulin test (TSI), which provide additional insights into thyroid function.

In some cases, you may receive a thyroid scan and/or a radioactive iodine uptake test, which are often offered together—both tests require you to ingest a pill containing a tiny amount of radioactive iodine. Several hours later, a device placed near your thyroid (on top of the skin) measures how much radioactive iodine was absorbed by the gland. The results determine whether your thyroid function is low, normal, or overactive. This will help determine the cause of thyroid overactivity.

Additionally, a thyroid ultrasound (which involves imaging of the thyroid gland using sound waves emitted by a probe) can be done to look for overactive thyroid nodules and to assess blood flow within the thyroid gland.

In general, medication helps most patients manage their condition. However, other treatments are also available if medication isn’t helpful.

Hyperthyroidism treatments include:

• Antithyroid drugs, such as propylthiouracil or methimazole, help to minimize the effects of the extra thyroid hormone in your system.
• Beta-blockers, such as metoprolol or propranolol, help manage the symptoms of hyperthyroidism, such as nervousness, a rapid heartbeat, and/or hand tremors. It’s important to note that this medication does not treat hyperthyroidism; it only relieves symptoms.
• Radioactive iodine, which destroys the thyroid, thereby stopping the excess production of thyroid hormone
• Surgery, during which the thyroid gland is removed, permanently stopping the production of thyroid hormone.

Patients treated with radioactive iodine or surgery to remove the thyroid must take synthetic thyroid hormone medication for the rest of their lives.

Some hyperthyroid treatments are considered unsafe for pregnant women or women who hope to become pregnant soon. If you take methimazole, for example, talk to your doctor about switching to a different medication (propylthiouracil) before trying to conceive. Radioactive iodine is also unsafe for pregnant women and those who plan to conceive in the near future. If you have had the treatment recently, your doctor might recommend delaying conception for six months.

Untreated hyperthyroidism can cause pregnancy complications, so it is important to treat your thyroid condition prior to pregnancy.

Undiagnosed, untreated hyperthyroidism may lead to a number of complications, including irregular heartbeat (atrial fibrillation), which can cause blood clots, stroke, and heart failure; osteoporosis; muscle weakness; and difficulty conceiving.

The treatments described above are usually helpful in managing hyperthyroidism, regardless of its cause, to the extent that the condition is considered well controlled.

“At Yale, we have a multidisciplinary team of endocrinologists, endocrine surgeons, radiologists, and nuclear medicine staff who work under a single roof to evaluate, diagnose, and comprehensively manage thyroid conditions,” says Yale Medicine endocrinologist Priyadarshini Balasubramanian, MD. “Our team of physicians works with you to provide you with an individualized treatment plan to ensure the best possible outcome.”