Graves’ disease is an autoimmune disease that affects the thyroid. The thyroid is a small gland in the front of the neck. It makes hormones called T3 and T4 that regulate how the body uses energy. Thyroid hormone levels are controlled by the pituitary, which is a pea-sized gland in the brain. It makes thyroid stimulating hormone (TSH), which triggers the thyroid to make thyroid hormone.  

With Graves’ disease, the immune system makes antibodies that act like TSH, causing the thyroid to make more thyroid hormone than your body needs. This is called an overactive thyroid or hyperthyroidism. An overactive thyroid causes every function of the body to speed up, such as heart rate and the rate your body turns food into energy. Graves’ disease is one cause of overactive thyroid. It is closely related to Hashimoto’s disease, another autoimmune disease affecting the thyroid.