The thyroid -- a butterfly-shaped gland at the base of the neck, just below the Adam's apple -- produces hormones that regulate heart rate, body temperature and energy level. Below is a list of benign thyroid disorders that can develop when those levels go out of whack. Most are diagnosed using a physical exam, thyroid scan, symptom history or blood work to measure thyroid hormone levels.

Hyperthyroidism, or overactive thyroid, occurs when your body overproduces thyroid hormones. Symptoms: weight loss, irritability, nervousness, racing heart, hand tremors and difficulty sleeping. Treatment: anti-thyroid drugs, which keep the gland from making new thyroid hormone); radioactive iodine treatment (given in capsule or liquid form, destroys overactive thyroid cells, repeat treatments may be needed); surgery (where most of the thyroid is removed), and beta-blocker drugs (which ease heart rate, the shakes and nervousness).

Hypothyroidism, or underactive thyroid, occurs when your body doesn't produce enough thyroid hormone. Symptoms: weight gain, dry skin or hair, feeling sluggish, depressed, cold, constipated or tired. Treatment: daily thyroid hormone replacement medication. Patients should follow up with their doctors because finding the right dose of medication is key to improvement. Not enough medication can keep levels too low; too much can cause hyperthyroidism symptoms.

Graves' disease, an autoimmune disorder that is the most common cause of hyperthyroidism. Symptoms and treatment: same as hyperthyroidism, above. Other symptoms: bulging of the eyes, eye inflammation, swelling around the eyes, double vision.

Hashimoto's disease, an autoimmune disorder that is the most common cause of hypothyroidism. Also called lymphocytic thyroiditis. Causes inflammation that impairs the thyroid's ability to produce hormones. Is also the most common cause of goiter, or enlargement of the thyroid. Symptoms and treatment: same as hypothyroidism.

-- January W. Payne

Sources: American Thyroid Association and the Mayo Clinic