The thyroid--a small, butterfly-shaped gland located below the Adam's apple that controls the body’s metabolism--malfunctions for many reasons, including low or high activity. Many people have mild thyroid disease and don't realize it's the reason for difficulties they experience. An overactive or underactive thyroid leads to a number of health problems. Most associated conditions can be managed or prevented with proper treatment.
Swollen Thyroid
Medical professionals refer to an enlarged thyroid as goiter. It results from most thyroid problems, including overactive and underactive thyroid, according to MayoClinic.com. Although painless, if it's large, a goiter makes a person cough and interferes with swallowing and breathing. Hoarseness is another side effect.
Fatigue
Fatigue is caused by an overactive and underactive thyroid, according to MayoClinic.com. Because fatigue is associated with many disorders, people may not realize they have a thyroid problem.
Muscle Weakness and Aches
An overactive or underactive thyroid causes muscle weakness, most often in the lower extremities, according to MayoClinic.com. Muscle aches and stiffness--especially in the shoulders or hips--also occurs with an overactive thyroid.
Heart Problems
Heart problems are a serious side effect of overactive and underactive thyroid, according to MayoClinic.com. For an overactive thyroid, these include a rapid or irregular heartbeat and, rarely, congestive heart failure--which means your heart isn't pumping enough blood. People with an underactive thyroid may have an enlarged heart and heart failure as well.
Birth Defects
Babies born to women with untreated Hashimoto’s disease--an underactive thyroid due to immune system disorder--may develop birth defects, including heart and brain problems, according to MayoClinic.com. Developmental and kidney problems are another side effect. Some doctors suspect that an underactive thyroid during pregnancy leads to cleft palate.
Eye Problems
Eye problems--including bulging and red eyes, oversensitivity to light and faulty vision--are a side effect of an overactive thyroid, says MayoClinic.com. Eye side effects usually develop about six months after a diagnosis of Graves' disease, a type of hyperthyroidism, according to Thyroid.org.
