An overactive thyroid, also known as hyperthyroidism, is a condition in which the thyroid gland produces excessive amounts of thyroid hormones. This can lead to symptoms such as weight loss, increased heart rate, anxiety, irritability, and heat intolerance. The cause of overactive thyroid may be due to various reasons including autoimmune disorders like Graves' disease or Hashimoto's thyroiditis, inflammation of the thyroid gland (thyroiditis), excessive iodine intake, or certain medications. Treatment options for hyperthyroidism include antithyroid medications, radioactive iodine therapy, and surgery to remove part or all of the thyroid gland.