Thyroid stimulating hormone is a hormone secreted by the pituitary gland in the human brain, which mainly plays a role in regulating the secretion of thyroid hormones. Once there is too much thyroid hormone in the body, thyrotropin will decrease. Thyrotropin is the main hormone in the body that regulates the production of thyroid hormone by the thyroid gland. When the body secretes more thyroid hormone, the pituitary gland secretes less thyrotropin; but when it secretes less thyroid hormone, the pituitary gland increases thyrotropin secretion to stimulate the thyroid gland to secrete more thyrotropin. Such non-stop changes maintain thyroxine at a stable level to meet the body’s physiological function needs. This is actually a negative feedback regulation mechanism of hormone secretion. The most common clinical condition in which thyroid stimulating hormone is reduced is hyperthyroidism. Hyperthyroidism leads to an increase in thyroid hormone secretion, and through a series of complex mechanisms, this information is fed back to the pituitary gland, which then reduces the secretion of thyroid stimulating hormone to achieve the purpose of reducing thyroid hormone secretion in order to alleviate a series of pathological changes brought about by hyperthyroidism in the human body. It can play a certain protective role for the human body. In addition, for some hypothyroid patients, due to insufficient secretion of thyroid hormones, long-term supplementation of thyroxine medication is required for treatment. This will also increase the level of thyroxine in the body. The pituitary gland also senses this change precisely to reduce the secretion of thyroid stimulating hormone. In general, low thyroid stimulating hormone is a change in hormone secretion due to increased levels of thyroxine in the body. The occurrence of this change is most often seen in patients with hyperthyroidism.