Thyroid-stimulating hormone or TSH is a naturally occurring hormone produced by the pituitary that stimulates the production of thyroid hormones. TSH is, in turn, regulated by the release of TRH (which increases TSH) and Somatostatin (which decreases TSH) by the hypothalmus. In patients beign treated with thyroid medications, doctors will be more likely to monitor TSH levels rather than thyroide hormone levels as this level is actually to be more likely to indicate whether the thyroid is working properly. Recently, synthetic TSH has been developed and is used in the treatment of thyroid cancer.