What is Overactive thyroid (hyperthyroidism)?

Hyperthyroidism occurs when the thyroid gland produces too much thyroid hormone, speeding up the body's metabolism. The most common cause is Graves' disease, an autoimmune condition, though thyroid nodules and inflammation can also be responsible.

Common symptoms include weight loss despite a normal or increased appetite, a rapid or irregular heartbeat, anxiety, tremor, heat intolerance, sweating, and difficulty sleeping. Some people also notice bulging eyes or a swelling in the neck (goitre).