The thyroid gland produces the hormones thyroxine, or T4, and triiodothyronine, or T3. The thyroid hormones circulate in the bloodstream and act on nearly all body tissues, influencing the pace of activity, or metabolism. Too much T4 and T3 characterizes the condition known as hyperthyroidism. Side effects associated with abnormally elevated thyroid hormone levels involve a variety of organ systems. Approximately one in every 100 people in the United States has hyperthyroidism, according to the American Association of Clinical Endocrinologists.
Insomnia, Nervousness and Irritability
Patients with excess T4 typically also have an elevated level of T3. Excess T4 and T3 cause a hyperexcited mental state, leading to nervousness and irritability, reports surgeon and endocrinologist James Norman, M.D., on the medical information website EndocrineWeb. The effect of the elevated thyroid hormone levels resembles the feeling experienced after consuming excessive amounts of caffeine. Because the excited mental state proves continuous, patients commonly experience chronic insomnia.
Hand Tremor
Patients with excess thyroid hormones commonly exhibit hand tremors. The Cleveland Clinic reports that the tremors characteristically occur with hand movements or when the patient attempts to maintain the hands in a specific position. Medical professionals describe the tremor associated with hyperthyroidism as a "fine" tremor, meaning the hands appear shaky as opposed to flapping broadly.
Increased Sweating and Heat Intolerance
The bodies of patients with hyperthyroidism generate excess heat due to the abnormally increased metabolic rate. People with excess T4 and T3, therefore, commonly experience increased sweating --- one of the body's primary cooling mechanisms. Similarly, patients with elevated thyroid hormone levels find warm environments uncomfortable, notes Merck Manuals Online Medical Library.
Unintentional Weight Loss
Patients with elevated T4 and T3 levels often experience unintentional weight loss, notes the National Institute of Diabetes and Digestive and Kidney Diseases. Weight loss occurs due to the accelerated rate of metabolism, which causes an increase in the number of calories required by the body. Patients typically report a normal or increased appetite.
Muscle Weakness
Hyperthyroidism commonly causes muscle weakness, especially in the thighs and upper arms, notes the American Thyroid Association. Muscle weakness leads to easy fatigability with physical exertion.
Menstrual Irregularity
Excessive T4---whether produced by the thyroid gland or caused by too much thyroid hormone replacement medication---can lead to menstrual irregularities, reports the American Association of Clinical Endocrinologists. Excess thyroid hormone interferes with the production and release of the hormones that control the menstrual cycle, typically leading to irregular periods or a temporary cessation of menstruation.
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