Possible causes of an overactive thyroid, or hyperthyroidism, include Graves' disease, thyroiditis, a thyroid nodule or too much iodine levels in the body, according to WebMD. Taking excessive thyroid hormone medications can also lead to the disorder.
In patients with the autoimmune condition Graves' disease, the immune system produces an antibody that triggers an overproduction of thyroid hormone, leading to hyperthyroidism, explains WebMD. Thyroiditis results from an immune system problem or a virus that causes swelling of the thyroid gland, which can result in thyroid hormone leaking into the bloodstream.
In patients with a single toxic nodule, the culprit that causes hyperthyroidism is one nodule growing in the thyroid gland that slowly boosts the thyroid hormone levels in the blood, notes WebMD. Those with toxic multinodular goiter have several nodules that make the thyroid overactive. Consumption of too much iodine can also lead to hyperthyroidism, because the body uses iodine to create the thyroid hormone.
If a patient is taking prescription thyroid medications, it is essential to avoid taking an extra dose without consulting a physician, WebMD advises. The common symptoms of hyperthyroidism include an enlarged thyroid, protruding eyes, double vision and sleeping trouble. Anxiety, hair problems and menstrual cycle changes are also symptoms of the disorder. Diagnosis of hyperthyroidism involves blood tests, a thyroid ultrasound, a thyroid scan or a radioactive iodine uptake test.