Normal cortisol levels in your blood range from 10 to 20 mcg/dL in the early morning and drop to 3 to 10 mcg/dL by late afternoon. Those numbers shift dramatically throughout the day because cortisol follows a built-in 24-hour cycle, peaking shortly after you wake up and falling to its lowest point around bedtime. Understanding this rhythm is key to interpreting any cortisol test result.
How Cortisol Changes Throughout the Day
Cortisol doesn’t hold steady. It follows one of the strongest daily rhythms of any hormone in your body. Levels are already high when you wake up, then surge another 50 to 60% in the 30 to 40 minutes after waking. This burst, sometimes called the cortisol awakening response, is what helps you feel alert and ready to start the day.
After that morning spike, cortisol drops quickly over the next few hours, then continues a slower decline through the afternoon and evening. By bedtime, levels hit their lowest point. This pattern means that a blood draw at 7 a.m. and one at 4 p.m. will produce very different numbers, and both can be perfectly normal. Any cortisol test result only makes sense when you know when the sample was taken.
Normal Ranges by Test Type
There are three main ways to measure cortisol, and each has its own reference range.
- Blood test (serum cortisol): Typically drawn between 6 a.m. and 8 a.m., when levels are highest. The normal range at that time is 10 to 20 mcg/dL. By around 4 p.m., normal drops to 3 to 10 mcg/dL.
- Saliva test: Usually collected late at night, when cortisol should be at its lowest. A late-night salivary cortisol above roughly 2.25 nmol/L raises suspicion for excess cortisol production. Saliva tests are convenient because you collect the sample at home.
- 24-hour urine test: You collect all urine over a full day so the lab can measure total cortisol output. The normal range for adults is 3.5 to 45 mcg per 24 hours.
Your doctor may order more than one type of test, or repeat the same test, because a single result can be thrown off by stress, illness, or timing. No one measurement tells the full story.
What Can Throw Off Your Results
Several things can push cortisol readings higher or lower without reflecting a true hormonal problem. The most common culprit is steroid medications. Long-term use of glucocorticoids (prescribed for conditions like asthma, arthritis, or autoimmune diseases) raises cortisol levels, and suddenly stopping them can cause levels to plummet. Birth control pills also affect cortisol measurements because they increase a protein in the blood that binds to cortisol, making total levels look higher than they functionally are.
Stress, poor sleep, intense exercise, and even the anxiety of a blood draw can all temporarily spike cortisol. If you’re getting a saliva test, your doctor may ask you to stop certain medications or topical creams beforehand. Always let your provider know about everything you’re taking, including supplements and skin products, before any cortisol test.
Signs of High Cortisol
When cortisol stays elevated for weeks or months, a pattern of symptoms starts to emerge that doctors recognize as Cushing syndrome. The most distinctive signs include weight gain concentrated in the face and belly, fatty deposits between the shoulder blades, and wide purple stretch marks across the abdomen. These stretch marks look different from the pinkish ones that come with normal weight gain or pregnancy. They’re broader and distinctly purple or reddish.
Other effects of sustained high cortisol include muscle weakness (particularly in the upper arms and thighs), high blood sugar that can progress to type 2 diabetes, high blood pressure, weakened bones prone to fractures, and excessive hair growth in women. The combination matters more than any single symptom. Many people have one or two of these issues for unrelated reasons, but the cluster together is what points toward a cortisol problem.
What Causes Cortisol to Stay Too High
The most common cause is actually external: long-term use of prescription steroid medications. When you take glucocorticoids for months or years, your body ends up with more cortisol activity than it needs, producing the same effects as if your own glands were overproducing.
When the cause comes from inside the body, the usual suspect is a small, noncancerous tumor on the pituitary gland. This tiny gland at the base of the brain sends signals telling your adrenal glands how much cortisol to make. A tumor there can send those signals constantly, driving cortisol production up. Pituitary tumors account for about 8 out of 10 cases of internally caused Cushing syndrome. Less commonly, a tumor on one of the adrenal glands themselves can produce excess cortisol directly. In rare cases, tumors elsewhere in the body (often in the lungs) can produce the same signaling hormone the pituitary uses, tricking the adrenal glands into overproduction.
Signs of Low Cortisol
Low cortisol, known as adrenal insufficiency, produces a different set of problems. The hallmark symptoms are persistent fatigue that doesn’t improve with rest, unintentional weight loss, loss of appetite, and low blood pressure. These symptoms tend to develop gradually, which makes them easy to dismiss or attribute to stress, poor diet, or aging. Some people also experience dizziness when standing, nausea, or darkening of the skin, particularly in skin creases and scars.
What Causes Cortisol to Stay Too Low
The most common form, called Addison’s disease, happens when the immune system mistakenly attacks the adrenal glands. Autoimmune damage accounts for 8 or 9 out of every 10 cases of Addison’s disease in developed countries. Certain infections, particularly tuberculosis and those associated with HIV/AIDS, can also damage the adrenal glands enough to impair cortisol production. Less common causes include cancer that spreads to the adrenal glands, surgical removal of the glands, or bleeding into them.
There’s also a secondary form where the problem isn’t with the adrenal glands at all but with the pituitary gland. Anything that disrupts the pituitary’s ability to send signals to the adrenals, including pituitary tumors, head injuries, autoimmune diseases, or surgery on the pituitary, can leave cortisol production chronically low. This secondary form is actually more common than Addison’s disease, partly because abruptly stopping long-term steroid medications suppresses the pituitary’s signaling ability, sometimes for months.
How Doctors Interpret Your Results
A single cortisol number, whether high or low, is rarely enough to diagnose anything. Doctors look at the timing of the test, your symptoms, your medication history, and often repeat the test or combine multiple testing methods. A morning blood cortisol below 3 mcg/dL strongly suggests adrenal insufficiency, while a level above 15 to 18 mcg/dL generally rules it out. Values in between require further testing.
For suspected high cortisol, doctors often start with a late-night salivary cortisol test or a 24-hour urine collection because these capture cortisol at a time or over a period when abnormalities are easier to detect. If results come back elevated on at least two separate occasions, additional testing can pinpoint whether the source is the pituitary, the adrenal glands, or something else entirely.
If your cortisol results come back outside the normal range but you feel fine and aren’t on steroid medications, the most likely explanation is a testing artifact: a stressful morning, a mistimed sample, or a medication interaction. Repeat testing under controlled conditions usually clarifies the picture.