|Thyroid-stimulating hormone (TSH)||
Thyroid-stimulating hormone (TSH) is made in the pituitary gland in your brain and controls the production of thyroxine and triiodothyronine. When the level of thyroxine and triiodothyronine in your blood are normal, your pituitary gland stops releasing TSH. When the level of thyroxine or triiodothyronine drops, the pituitary gland produces more TSH to boost the level.
Definition from NHS Choices: Thyroid-stimulating hormone (TSH)