Thyroid disease refers to a range of conditions that affect the thyroid gland, which is located in the neck and produces hormones that regulate metabolism, growth, and development. There are several types of thyroid diseases including hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), Graves' disease, Hashimoto's thyroiditis, thyroid cancer, and other rare disorders. These conditions can cause a variety of symptoms such as fatigue, weight gain or loss, sensitivity to cold, rapid heartbeat, tremors, and more. Treatment for thyroid diseases may involve medication, surgery, or radiation therapy depending on the specific condition.