The opposite of
hypothyroidism.
A condition in which the thyroid gland overproduces thyroid hormones resulting in many negative symptoms, including loss of weight and heart palpatations.
Due to the stress it places on the heart, it is often treated with radioactive iodine, destroying the thyroid gland. This gives the patient hypothyroidism, which is much less dangerous.
see also: thyroiditis, Hashimoto's thyroiditis, Graves' disease