what causes the thyroid gland not to function properly
1 These hormones regulate the body's metabolism. 2  The thyroid gland is stimulated by the hypothalamus and the pituitary gland. 3  Hypothyroiditis can occur if the thyroid gland does not function correctly, or if it is not stimulated properly. 4  The most common cause of hypothyroidism in the US is Hashimoto's disease.ypothyroidism is a condition that occurs when the thyroid gland does not produce enough thyroid hormones to meet the needs of the body. The thyroid creates two thyroid hormones, triiodothyronine (T3) and thyroxine (T4) that regulate metabolism. They also affect the following: 1.