What is Cortisol?
Cortisol is the body's primary stress hormone, produced by the adrenal glands. It regulates the stress response, blood sugar, immune function, anti-inflammatory processes, and metabolism.
Cortisol has a pronounced diurnal rhythm — it is highest in the morning (around 8 AM) and lowest late at night. Results must always be interpreted relative to the time of blood draw. Dynamic tests (ACTH stimulation, dexamethasone suppression) are typically needed for diagnosis rather than a single level.
Why might Cortisol be low?
Low cortisol can indicate adrenal insufficiency (Addison's disease) or suppression from prior corticosteroid use. Symptoms can include fatigue, low blood pressure, salt craving, and weight loss. Early morning cortisol is the most informative single measurement.
This information is educational. A single out-of-range result is rarely the whole picture — a healthcare professional can interpret your numbers alongside your overall health and history.
Context questions that matter
- →Was this result slightly or clearly outside the reference range?
- →Were related markers also high or low?
- →Is this new compared with previous tests?
- →Could recent illness, exercise, fasting, alcohol, supplements, or medication affect it?
- →Do you have symptoms that should be discussed with a clinician?
Questions to ask your doctor
- →Could time of day, cycle phase, stress, sleep, medication or supplements affect this result?
- →How does this compare with related hormones such as LH, FSH, testosterone, estradiol, prolactin, cortisol or DHEA-S?
- →Is this a one-time result, or part of a pattern that needs repeat testing?
Don't guess from one flagged result.
Start with the most relevant panel and see how your markers fit together in plain English.
Frequently asked questions
What does low Cortisol mean?
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Low cortisol can indicate adrenal insufficiency (Addison's disease) or suppression from prior corticosteroid use. Symptoms can include fatigue, low blood pressure, salt craving, and weight loss. Early morning cortisol is the most informative single measurement.
What is Cortisol?
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Cortisol is the body's primary stress hormone, produced by the adrenal glands. It regulates the stress response, blood sugar, immune function, anti-inflammatory processes, and metabolism.
Does timing matter for hormone tests?
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Often yes. Time of day, menstrual cycle phase, sleep, acute stress, medications and supplements can all affect hormone results. Morning samples and same-time-of-day repeat testing are typically preferred for hormones with a daily rhythm.
Should hormone results be compared with related hormones?
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Yes — hormones are usually interpreted as patterns. TSH is read with Free T4 and Free T3; testosterone is read with LH, FSH and SHBG; cortisol is read with ACTH and the time of day. Single values out of context can be misleading.