Thyroid hormone, one of the most commonly used medications among the elderly, was once prescribed for obesity, hypertension, and sterility. Today, however, its use is limited to disorders of the thyroid such as thyroid cancer or thyroid deficiency. Unfortunately, a recent survey revealed that 29% of men and 12% of women taking thyroid hormone are not taking it for the appropriate reasons. Taking thyroid hormone when it is not needed can result in hyperthyroidism, which is characterized by nervousness, hypersensitivity to heat, palpitations, insomnia, and weakness. Too much of the hormone may also resuit in osteoporosis. Many of those taking the medication for the wrong reasons had it prescribed many years ago and have not been reassessed by their physicians. Along with the people who take the medication unnecessarily, one third of those who need to take it are being undertreated [Dean's Rounds: Tufts University School of Medicine 1989; Fall:3].