Over 20 million people in the United States suffer from thyroid disorders, according to the American Thyroid Association. Located at the base of the neck, the thyroid gland produces hormones that control critical processes in the body, including metabolism. If it doesn't make enough thyroid hormones, the result is a condition called hypothyroidism, or an underactive thyroid. The treatment for this is pills containing synthetic thyroid hormone. The goal of treatment is to take just enough medication to achieve normal thyroid hormone effects in the body. But if too much thyroid medication is taken, symptoms will occur that are similar to those of an overactive thyroid, or hyperthyroidism.
Heat Intolerance and Sweating
Excessive thyroid hormone speeds up the body’s overall metabolism. This causes the body to produce more heat, leading to heat intolerance. This will cause a person to feel much hotter than other people in warm environments. As the body responds to the increased heat production, it tries to compensate by sweating -- a natural cooling mechanism. Sweating and heat intolerance are often some of the earliest symptoms of too much thyroid medication.
Other common symptoms of too much thyroid hormone involve the heart. Excessive thyroid hormone causes the heart to pump faster and harder. This may be felt as racing or pounding palpitations in the chest. Atrial fibrillation, an irregular heart rhythm, may also occur. Less often, chest pain develops. This is generally caused by insufficient blood reaching the heart muscle because of the fast heart rate. It is more common in people with heart disease. A fast heart rate or atrial fibrillation may also lead to heart failure, causing such symptoms as shortness of breath and ankle swelling.
Digestive System Effects
As too much thyroid hormone increases metabolism, the body requires more energy. To compensate, the person’s appetite increases, but weight will often decrease although the person eats more. Frequent bowel movements are another relatively common symptom of too much thyroid hormone. Upper abdominal pain, nausea and belching may also occur. Difficulty with swallowing is a possible, although uncommon, effect of excessive thyroid hormone.
People who take too much thyroid hormone may feel anxious, jittery and irritable. They may suffer from insomnia, finding it difficult to get to sleep or stay asleep. Tremors, especially of the hands, can become noticeable as well. Fatigue and muscle weakness are relatively common symptoms of too much thyroid hormone. Hair loss and difficulty concentrating may sometimes occur. In women, menstrual flow may decrease or even stop. Prolonged use of too much thyroid medication may lead to osteoporosis, producing thin bones that are prone to painful fractures.
Warnings and Precautions
If you have any symptoms of too much thyroid medication, see your physician. Blood tests can be taken to determine whether this is the cause of your symptoms. If you have taken a large amount of thyroid hormone medication over a short period of time -- as in an acute overdose -- seek immediate medical care. Life-threatening thyroid storm can occur in this situation, producing large increases in heart rate, blood pressure and temperature, as well as seizures, confusion and even coma or death.
Reviewed and revised by: Mary D. Daley, M.D.