Any problem with the butterfly-shaped gland at the base of the neck, called the thyroid.

The thyroid gland makes hormones that control how the body changes food and drink into energy — a process called metabolism. Many thyroid diseases happen when the gland releases too many or too few hormones. Other thyroid problems include cancer, growths called nodules, and an enlarged thyroid, called goiter.

Symptoms depend on what causes a thyroid problem. Too much thyroid hormone, called hyperthyroidism, can cause nervousness, weight loss, irregular heartbeat and sleep problems. Too little thyroid hormone, called hypothyroidism, can cause tiredness, dry skin and muscle weakness. A growth on the thyroid, called a nodule, may cause no symptoms.

Treatments depend on the cause. They often involve restoring thyroid hormone to the usual levels. Treatment can involve medicines and sometimes surgery.