Evidence check: FT4 in the context of stress

FT4 (free thyroxine) is a thyroid hormone that can be influenced by stress via the HPA axis. Acute stress typically lowers TSH while FT4 remains relatively stable; chronic stress may cause subtle shifts, but evidence is moderate and inconsistent. A single FT4 value without TSH and clinical symptoms is insufficient for stress assessment. Consumer blood tests measure FT4 accurately, but interpretation requires clinical context because many factors (time of day, medications, diet) affect levels. Claims that FT4 alone is a stress marker are overstated. Evidence: human-moderate. Caveat: Do not use isolated FT4 to diagnose stress; always evaluate with TSH, fT3, and clinical presentation.