Elevated circulating thyroid hormones suppress pituitary secretion of thyroid-stimulating hormone through negative feedback mechanisms, and reduced thyroid-stimulating hormone levels result in unregulated synthesis of thyroid hormones.

Study: An Abnormality of Thyroid Hormone Receptor Expression May Explain Abnormal Thyrotropin Production in Thyrotropin-Secreting Pituitary Tumors

When the thyroid gland makes too much hormone, the brain usually tells it to slow down — but in these tumors, the brain’s ‘off switch’ is broken because the cells can’t read the hormone signal. This proves the normal system works the way the claim says.

Study: Interrelationships in the regulation of TSH and prolactin secretion in man: effects of L-dopa, TRH and thyroid hormone in various combinations.

When there's too much thyroid hormone in the blood, the brain turns down the signal (TSH) that tells the thyroid to make more — this study shows that happening. Less TSH means the thyroid slows down, which is how the body keeps hormone levels balanced.

Study: Fundamentally distinct roles of thyroid hormone receptor isoforms in a thyrotroph cell line are due to differential DNA binding.

When there’s too much thyroid hormone in the body, a specific protein in the pituitary gland (THRB) tells it to stop making TSH, which in turn slows down thyroid hormone production. This study shows exactly how that off-switch works at the cellular level.