Overactive thyroid (also known as hyperthyroidism) is a relatively common hormonal condition that occurs when there is too much thyroid hormone in the body. Excess levels of thyroid hormones can then speed up the body’s metabolism, triggering a range of symptoms, such as: nervousness and anxiety hyperactivity – where a person can’t stay still and is full of nervous energy unexplained or unplanned weight loss swelling of the thyroid gland, which causes a noticeable lump, known as a goitre, to form in the throat The severity, frequency and range of symptoms can vary from person to person.