Is FT4 useful for stress?

FT4 (free thyroxine) is a thyroid hormone used primarily to assess thyroid function, not directly for stress. Chronic stress can affect the thyroid axis via the HPA axis (e.g., low T3, normal FT4), but FT4 alone is not an established stress biomarker. For stress assessment, cortisol, DHEA, or heart rate variability are more appropriate. A MyBody-X test measuring FT4 provides only an indirect clue if thyroid dysfunction is present. Evidence for FT4 as a stress marker is weak (practice/unclear). Caveat: Without medical interpretation, an isolated FT4 value can be misleading. For stress symptoms, consult a doctor for proper testing.