An abnormality of the thyroid gland characterized by the pathologically excessive production of thyroid hormones; -- also, the resulting condition characterized by increased metabolism, weight loss, rapid heart rate, high blood pressure, an enlarged thyroid gland and sometimes exophthalmos. It leads to, and may be confirmed by, high plasma levels of triiodothyronine or thyroxin.
Hyperthyroidism is a condition caused by an over-active thyroid gland which secretes greater-than-normal amounts of thyroid hormones. Symptoms include nervousness, constant hunger, weight loss and tremors. Scientists do not believe hyperthyroidism is caused by radiation exposure.