The thyroid gland uses iodine to produce thyroid hormones that regulate body metabolism. Thyroid agents either replace or remove hormones to prevent deficiency and excess. Thyroid agents include thyroid hormones (T3, T4, TSH)and antithyroid drugs (further classified as thioamides and iodine solution).
The major endocrine organs of the body include the pituitary, thyroid, parathyroid, adrenal, pineal and thymus glands, the pancreas, and the gonads. The regulatory functions of the nervous and endocrine systems are similar in some aspects, but differ in such ways.