Hyperthyroidism is a condition of the thyroid. The thyroid is a small, butterfly-shaped gland located at the front of your neck. It produces tetraiodothyronine (T4) and triiodothyronine (T3), which are two primary hormones that control how your cells use energy. Your thyroid gland regulates your metabolism through the release of these hormones.

Hyperthyroidism occurs when the thyroid makes too much T4, T3, or both. Diagnosis of overactive thyroid and treatment of the underlying cause can relieve symptoms and prevent complications.

What causes hyperthyroidism?

A variety of conditions can cause hyperthyroidism. Graves’ disease, an autoimmune disorder, is the most common cause of hyperthyroidism. It causes antibodies to stimulate the thyroid to secrete too much hormone. Graves’ disease occurs more often in women than in men. It tends to run in families, which suggests a genetic link. You should tell your doctor if your relatives have had the condition.

Other causes of hyperthyroidism include:

excess iodine, a key ingredient in T4 and T3thyroiditis, or inflammation of the thyroid, which causes T4 and T3 to leak out of the glandtumors of the ovaries or testesbenign tumors of the thyroid or pituitary glandlarge amounts of tetraiodothyronine taken through dietary supplements or medication

What are the symptoms of hyperthyroidism?

High amounts of T4, T3, or both can cause an excessively high metabolic rate. This is called a hypermetabolic state. When in a hypermetabolic state, you may experience a rapid heart rate, elevated blood pressure, and hand tremors. You may also sweat a lot and develop a low tolerance for heat. Hyperthyroidism can cause more frequent bowel movements, weight loss, and, in women, irregular menstrual cycles.

Visibly, the thyroid gland itself can swell into a goiter, which can be either symmetrical or one-sided. Your eyes may also appear quite prominent, which is a sign of exophthalmos, a condition that’s related to Graves’ disease.

Other symptoms of hyperthyroidism include:

increased appetitenervousnessrestlessnessinability to concentrateweaknessirregular heartbeatdifficulty sleepingfine, brittle hairitchinghair lossnausea and vomitingbreast development in men

The following symptoms require immediate medical attention:

dizzinessshortness of breathloss of consciousnessfast, irregular heart rate

Hyperthyroidism can also cause atrial fibrillation, a dangerous arrhythmia that can lead to strokes, as well as congestive heart failure.