Is Cortisol useful for fatigue?

Cortisol is a key stress hormone, and its measurement can be useful when there is clinical suspicion of adrenal insufficiency or Cushing's syndrome. However, for general fatigue without specific symptoms, a cortisol test is not recommended as a routine screening tool. Many direct-to-consumer tests offer cortisol measurements, but interpretation is complex: values fluctuate with time of day, stress, diet, and sleep. Without medical guidance, such tests can lead to misinterpretation or unnecessary worry. The evidence for using cortisol testing in non-specific fatigue is weak; clinical guidelines reserve it for targeted endocrine evaluation. Therefore, cortisol alone is not a useful biomarker for general fatigue. If you suffer from persistent tiredness, consult a physician for a comprehensive workup including blood count, thyroid function, iron status, and vitamin D.