Your thyroid is a butterfly-shaped gland in your neck, just above your collarbone. It is one of your endocrine glands, which make hormones. Thyroid hormones control the rate of many activities in your body. These include how fast you burn calories and how fast your heart beats. All of these activities are your body's metabolism. If your thyroid is too active, it makes more thyroid hormones than your body needs. This is called hyperthyroidism.
Hyperthyroidism is more common in women, people with other thyroid problems, and those over 60 years old. Graves' disease, an autoimmune disorder, is the most common cause. Other causes include thyroid nodules, thyroiditis, consuming too much iodine, and taking too much synthetic thyroid hormone.
The symptoms can vary from person to person. They may include
To diagnose hyperthyroidism, your doctor will do a physical exam, look at your symptoms, and do thyroid tests. Treatment is with medicines, radioiodine therapy, or thyroid surgery. No single treatment works for everyone.
NIH: National Institute of Diabetes and Digestive and Kidney Diseases