Cortisol: Low vs High Signs, Testing, Energy, and Stress
Overview
Cortisol is one of the main stress hormones made by the adrenal glands. It helps you wake up, respond to physical and psychological stress, regulate blood sugar, and coordinate immune and inflammatory responses. In a healthy pattern, cortisol is highest in the morning and gradually falls across the day so that you can wind down and sleep.
Clinicians usually look at cortisol when there is long term fatigue, sleep and energy problems, symptoms that suggest very high or very low stress hormone states, or when investigating conditions that affect the adrenal glands or the hypothalamic pituitary adrenal axis. It is often interpreted together with morning cortisol labs so that symptoms and daily rhythm can be compared with measured values.
What Cortisol is and where it is made
Cortisol is a steroid hormone produced by the adrenal cortex, the outer layer of the adrenal glands that sit on top of the kidneys.
Its release is controlled by the hypothalamic pituitary adrenal axis. The hypothalamus releases CRH, the pituitary releases ACTH, and ACTH signals the adrenals to make cortisol.
Cortisol is released in pulses, with a strong daily rhythm that usually peaks in the early morning and is lowest around midnight in people who sleep at night.
What Cortisol does in your body
Helps mobilize and maintain blood sugar during stress or fasting by influencing glucose production and storage.
Supports blood pressure and cardiovascular responses so that blood can reach vital organs under stress.
Modulates immune and inflammatory activity, which can be protective in short bursts but problematic if levels stay high or very low over time.
Affects alertness, focus, and the feeling of being “switched on”, especially in the morning.
Interacts with sleep and circadian rhythms, influencing how refreshed or wired you feel at different times of day.
Responds to physical stressors such as illness, injury, surgery, and intense exercise, as well as psychological stress.
When testing Cortisol makes sense
Persistent fatigue, low morning energy, or feeling “tired but wired” late at night.
Suspicion of very high cortisol states, such as unexplained weight gain around the trunk, easy bruising, thin skin, or muscle weakness, when guided by a clinician.
Suspicion of very low cortisol states, such as severe chronic fatigue, weight loss, low blood pressure, or repeated episodes of feeling faint or unwell with minor illness.
Assessment of adrenal function in people using or tapering long term glucocorticoid medications such as prednisone.
Workup of some blood pressure problems, blood sugar instability, or unexplained changes in weight and mood.
Part of a broader evaluation of the stress system when symptoms, history, and medications raise concern.
How to think about high and low Cortisol results
This information is general and does not replace lab specific reference ranges, timing rules, or medical evaluation.
Low cortisol might be associated with:
Marked fatigue that does not improve with rest and that can worsen with minor illness.
Low blood pressure or dizziness on standing in more severe cases.
Unintentional weight loss, low appetite, or nausea.
Darkening of the skin or other signs when autoimmune adrenal disease is present.
Possible contributors include primary adrenal insufficiency, secondary adrenal insufficiency from pituitary or hypothalamic problems, or suppression of the adrenal axis after long term glucocorticoid medication use. This pattern is serious and requires careful medical evaluation rather than self management.
High cortisol might be associated with:
Weight gain, especially around the abdomen, face, and upper back.
Thinning skin, easy bruising, slow wound healing, and sometimes purple stretch marks.
High blood pressure, elevated blood sugar, and changes in lipids.
Sleep disruption, feeling constantly “on edge”, or mood changes such as anxiety, irritability, or low mood.
Possible contributors include chronic exposure to high dose glucocorticoid medications, rarely cortisol producing adrenal or pituitary tumors, chronic severe stress, depression, and medical illness. Timing errors, shift work, and some medications can also change measured cortisol, so results almost always need confirmation and context.
What can influence your Cortisol levels
Time of day and sleep schedule, including night shifts or frequent time zone changes.
Short term psychological stress, ongoing life stress, and how you recover between stressors.
Acute illness, surgery, infection, or significant inflammation.
Use of glucocorticoid medications such as prednisone, inhaled or topical steroids, and some joint injections.
Caffeine, alcohol, and very intense or prolonged exercise, especially late in the day.
Very low calorie intake, rapid weight loss, and underfueling relative to training.
Underlying endocrine conditions that affect the pituitary, adrenal glands, or thyroid.
The method of testing, such as blood, saliva, or urine, and whether samples are taken at the correct time.
When to talk to a clinician about Cortisol
Persistent, unexplained fatigue, especially if mornings feel very difficult for weeks to months.
Concerning weight changes, new high blood pressure, or blood sugar changes that do not have a clear explanation.
Physical signs that suggest very high or very low cortisol, such as easy bruising, thin skin, or repeated episodes of feeling faint or unwell with mild illness.
Long term use of steroid medications where you are unsure how they may affect adrenal function.
Ongoing sleep disturbance and stress symptoms that do not improve with basic changes and raise concern about your health.
A clinician can choose the right tests and timing, interpret cortisol patterns alongside other hormones and health conditions, and decide whether more specialized evaluation is needed.
Cortisol in one view
Cortisol is a central stress and circadian hormone that helps you maintain blood sugar, blood pressure, immune balance, and alertness, especially in the first part of the day. Problems arise when levels are very high, very low, or out of sync with your natural sleep wake cycle. A single cortisol result is most useful when it is drawn at the correct time, compared with morning patterns such as a measured cortisol awakening response, and considered alongside symptoms and other health data. For people working on stress and sleep, this often fits well with a structured circadian routine such as a Circadian Entrainment approach under the guidance of a clinician rather than self diagnosing adrenal problems.
