Hyperthyroidism (overactive thyroid) occurs when your thyroid gland produces too much of the hormone thyroxine. Hyperthyroidism can accelerate your body's metabolism, causing unintentional weight loss and a rapid or irregular heartbeat.

Symptoms

Hyperthyroidism can mimic other health problems, which can make it difficult for your doctor to diagnose. It can also cause a wide variety of signs and symptoms, including: Unintentional weight loss, even when your appetite and food intake stay the same or increase, Rapid heartbeat (tachycardia) — commonly more than 100 beats a minute, Irregular heartbeat (arrhythmia), Pounding of your heart (palpitations), Increased appetite, Nervousness, anxiety and irritability, Tremor — usually a fine trembling in your hands and fingers, Sweating, Changes in menstrual patterns, Increased sensitivity to heat, Changes in bowel patterns, especially more frequent bowel movements, An enlarged thyroid gland (goiter), which may appear as a swelling at the base of your neck, Fatigue, muscle weakness, Difficulty sleeping, Skin thinning, Fine, brittle hair. Older adults are more likely to have either no signs or symptoms or subtle ones, such as an increased heart rate, heat intolerance and a tendency to become tired during ordinary activities.

Causes

Thyroid glandOpen pop-up dialog box Hyperthyroidism can be caused by a number of conditions, including Graves' disease, Plummer's disease and thyroiditis. Your thyroid is a small, butterfly-shaped gland at the base of your neck, just below your Adam's apple. The thyroid gland has an enormous impact on your health. Every aspect of your metabolism is regulated by thyroid hormones.Your thyroid gland produces two main hormones, thyroxine (T4) and triiodothyronine (T3), that influence every cell in your body. They maintain the rate at which your body uses fats and carbohydrates, help control your body temperature, influence your heart rate, and help regulate the production of protein. Your thyroid also produces a hormone that helps regulate the amount of calcium in your blood (calcitonin).