Thyrotoxicosis is the name given to the clinical effects experienced due to an excess of thyroid hormones in the bloodstream. Hormones produced by the thyroid gland control how fast or slow the body works (metabolic rate). Too much thyroid hormone (thyroxine and triiodothyronine) speeds up the metabolism and results in the signs and symptoms of thyrotoxicosis

The main cause of thyrotoxicosis is hyperthyroidism, which is an overactivity of the thyroid gland resulting in it producing excess levels of thyroid hormones. If the hyperthyroidism is due to an autoimmune cause, it is called Graves' disease.

Other rarer causes of thyrotoxicosis include excessive intake of thyroid hormone in patients treated for hypothyroidism (an underactive thyroid gland) and sometimes, inflammation of the thyroid gland (thyroiditis), which causes release of large quantities of thyroid hormone into the bloodstream.

The symptoms of thyrotoxicosis are a result of the high levels of thyroid hormones in the blood, increasing the metabolic rate. These can include diarrhoea, weight loss (although around 10% develop weight gain due to increased appetite), shaking or tremor (notably in the hands), sweating, increased heart rate that can be felt by the patient (palpitations), overactivity, agitation, anxiety, changes in emotions and feeling hot even though the room may feel cold to everyone else.

Patients may also experience an increased heart rate, thinning of the hair, swellings or nodules in the thyroid gland (goitre) or other signs of hyperthyroidism. Some signs are only seen in patients with Graves’ disease (an autoimmune cause) including thyroid eye disease, and rarely, skin changes on the legs and swellings of the finger tips.