The ability of the organism to flexibly preserve homeostatic equilibria in response to internal or environmental challenges is a sign of its healthy state. Thyroid hormones target a broad spectrum of metabolic effects. This requires them to be tightly controlled, as are their energetic and metabolic targets. The involvement of pituitary thyrotropin (TSH) in thyroid hormone control has long been recognised [1]. As a result, the measurement of TSH has been exploited for the diagnosis of thyroid disorders, particularly after highly sensitive TSH assays became available in the 1980s [2–4]. Despite being at best an indirect indicator of thyroid hormone homeostasis, TSH measurement has become a corner stone of contemporary thyroid function testing [5, 6].