Also known as thyrotoxicosis. Characterised by an elevated level of serum free thyroid hormone.

It can be caused by increased synthesis of thyroid hormone (whether originating from the pituitary issuing too much thyroid stimulating hormone or the thyroid itself or from weird things such as choriocarcinomas), excessive release of thyroid hormone (as in destruction of thyroid tissue in thyroiditis) or the conscious or accidental ingestion of excess thyroid hormone (thyrotoxicosis factitia).

The most common cause of hyperthyroidism is Graves' disease.

The common symptoms of hyperthyroidism include: goiter, tremor, nervousness, increased sweating, hypersensitivity to heat, palpitations, fatigue, increased appetite, weight loss, insomnia, weakness and frequent bowel motions (possibly even diarrhea).

All probable cases of hyperthyroidism should be brought to the attention of a competent doctor.