Hypothyroidism is the term for a slower-performing thyroid. This can decrease metabolism and cause chronic fatigue. A person may receive a diagnosis of hyperthyroidism if his thyroid produces too many T3 and T4 hormones; this leads to other hormone imbalances and a faster metabolism, sometimes causing rapid weight loss. Goiters are swollen thyroids, a painful condition that not only affects the thyroid itself but also the voice box and blood flow around the neck. Cancer of the thyroid is another disorder that can mimic hypothyroidism.

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