Your cortisol level is a measurement of how much cortisol, the body’s primary stress hormone, is circulating in your blood, saliva, or urine at a given time. A normal morning blood cortisol reading falls between 10 and 20 micrograms per deciliter (mcg/dL), measured between 6 a.m. and 8 a.m. By late afternoon, that number drops to 3 to 10 mcg/dL. Because cortisol follows a strict daily rhythm and responds to dozens of outside influences, understanding what the number means requires knowing when and how it was measured.
What Cortisol Does in Your Body
Cortisol is produced by the adrenal glands, two small organs sitting on top of your kidneys. It touches nearly every system in your body, but its three most important jobs involve blood sugar, inflammation, and blood pressure.
For blood sugar, cortisol tells the liver to produce glucose from stored fats and proteins, while simultaneously making muscles and fat tissue less responsive to insulin. The net effect is more sugar available in the bloodstream, which is useful during a genuine emergency but problematic when it stays elevated for weeks or months. Cortisol also amplifies the blood-sugar-raising effects of other hormones like adrenaline and glucagon.
For inflammation, cortisol works as a powerful off switch. It suppresses key inflammatory pathways in the immune system, dialing down both the rapid-response (innate) and long-term (adaptive) branches of immunity. This is why synthetic versions of cortisol are prescribed for autoimmune conditions like lupus and rheumatoid arthritis.
For blood pressure, cortisol promotes sodium retention in the kidneys, which pulls water into the bloodstream and raises pressure. It also makes blood vessels more sensitive to the tightening signals from adrenaline and blocks the production of molecules that normally keep vessels relaxed. Together, these effects raise vascular resistance throughout the body.
The Daily Cortisol Cycle
Cortisol doesn’t stay at one level throughout the day. It follows a predictable 24-hour rhythm. Levels hit their lowest point around midnight, then begin climbing between 2 a.m. and 3 a.m. while you’re still asleep. They peak around 8:30 a.m., which is part of what helps you feel alert in the morning. From there, cortisol gradually declines through the afternoon and evening, reaching that midnight low again.
This cycle is why the time of your blood draw matters enormously. A cortisol reading of 8 mcg/dL at 7 a.m. could signal a problem, but the same number at 4 p.m. would be perfectly normal. Any cortisol test result is essentially meaningless without knowing when the sample was collected.
How Cortisol Is Tested
There are three main ways to measure cortisol, and each one captures something slightly different.
- Blood test: The most common method. It measures total cortisol (both the active, unbound form and the portion bound to proteins). Morning draws between 6 and 8 a.m. are standard because that’s when levels are highest and most consistent between people.
- Saliva test: Reflects only the unbound, active cortisol in your system. Late-night salivary cortisol, collected around 11 p.m. to midnight, is particularly useful for screening for excess cortisol, since levels should be very low at that hour. If they’re not, it suggests the normal daily rhythm is disrupted.
- 24-hour urine test: You collect all urine over a full day, which gives an average picture of cortisol output rather than a single snapshot. This is commonly used to screen for conditions where cortisol stays too high around the clock.
A morning blood cortisol below 5 mcg/dL, combined with other hormone markers, is considered preliminary evidence of adrenal insufficiency. In a stimulation test, where a synthetic hormone is injected to challenge the adrenal glands, a peak cortisol below 18 mcg/dL at 30 or 60 minutes confirms the adrenals aren’t producing enough.
What Raises Cortisol Temporarily
Several everyday factors can push cortisol above your baseline, which is worth knowing if you’re preparing for a test or trying to interpret results.
Mental stress is the most obvious trigger. Interestingly, the cortisol response to psychological stress tends to be larger in men than in women. Caffeine alone, in the absence of stress, doesn’t appear to raise cortisol significantly. But caffeine combined with mental stress amplifies the cortisol spike beyond what stress alone would produce. The same pattern holds for exercise: moderate, short-duration physical activity doesn’t reliably increase cortisol as long as blood sugar stays stable, but intense or prolonged exercise pushes cortisol considerably higher. Caffeine taken before exercise also elevates cortisol in both men and women, even when exercise alone wouldn’t.
Sleep deprivation disrupts the normal daily rhythm and can keep cortisol elevated during hours when it should be falling. If you’re scheduled for a cortisol test, getting a normal night’s sleep and avoiding caffeine and intense workouts that morning will give the most accurate reading.
Signs of Chronically High Cortisol
When cortisol stays elevated for months, the physical effects become visible. Weight gain concentrates around the midsection and face (sometimes called “moon face”), while the arms and legs actually thin out from muscle wasting. Fat accumulates at the base of the neck and between the shoulder blades. Skin becomes fragile, bruising easily, and wide purple stretch marks may appear on the abdomen, breasts, hips, and underarms.
Women may notice excess hair growth on the face, chest, and abdomen, along with irregular or absent periods. Men may experience reduced sex drive and erectile dysfunction. Children with chronically high cortisol tend to gain weight while growing more slowly than their peers.
The most common cause of chronically elevated cortisol is long-term use of corticosteroid medications prescribed for conditions like asthma, rheumatoid arthritis, or lupus, or used after organ transplants. When the body itself overproduces cortisol, a condition called Cushing’s syndrome, the usual culprits are small, noncancerous pituitary tumors that send too many signals to the adrenal glands, tumors on the adrenal glands themselves, or rarely, tumors elsewhere in the body (most often the lungs) that produce the same signaling hormone.
Signs of Chronically Low Cortisol
Insufficient cortisol produces a different and equally disruptive pattern. The hallmark symptoms are persistent fatigue, muscle weakness, loss of appetite, and unexplained weight loss. Many people also experience nausea, abdominal pain, dizziness when standing (from low blood pressure dropping further), and strong cravings for salty foods. Low blood sugar episodes, irritability, depression, and loss of interest in sex are common.
People with Addison’s disease, the primary form of adrenal insufficiency, often develop noticeable darkening of the skin, especially on scars, skin folds, elbows, knees, knuckles, and the inside of the cheeks.
The single most common cause of low cortisol overall is abruptly stopping corticosteroid medications after taking them for a long time. When you take synthetic cortisol for weeks or months, your body dials back its own production. Stop suddenly and the adrenal glands can’t ramp back up fast enough.
When the adrenals themselves are damaged, it’s most often from autoimmune disease, which accounts for 8 or 9 out of every 10 cases of Addison’s disease in developed countries. The immune system attacks the adrenal glands and destroys their ability to make cortisol. Tuberculosis and HIV/AIDS are less common but recognized causes. Sometimes the problem originates not in the adrenal glands but in the pituitary gland in the brain, which controls how much cortisol the adrenals produce. Pituitary tumors, head injuries, infections, and certain genetic conditions can all disrupt this signaling chain and lead to cortisol deficiency even when the adrenal glands themselves are healthy.