How are FT4 and stress related?

FT4 (free thyroxine) and stress are linked via the hypothalamic-pituitary-adrenal (HPA) axis. Chronic stress elevates cortisol, which can suppress TSH secretion and reduce the conversion of T4 to active T3, potentially lowering FT4 levels or altering thyroid function. Evidence comes from human observational studies, not RCTs. The relationship is associative, not definitively causal, and individual responses vary. For thyroid patients, stress management is supportive, not a substitute for medical therapy. Genetic tests for thyroid function are not clinically validated.