Cortisol explained, and why "adrenal fatigue" is a myth

Cortisol is the body's main stress hormone, made by the adrenal glands, and it keeps you alert, fueled and able to respond to pressure. "Adrenal fatigue," the idea that chronic stress wears out your adrenals until they cannot make enough cortisol, is not a recognized diagnosis, and a systematic review of 58 studies found no evidence it exists. The exhaustion is real. The explanation is wrong, and believing it can send you toward the wrong fixes.

If you have been running a company for years and feel flat by 2 p.m., you have probably met the adrenal fatigue story somewhere: a podcast, a wellness site, a friend's supplement cabinet. Here is what cortisol actually does, what the research says, and what to look at instead.

What is cortisol and what does it do?

Cleveland Clinic describes cortisol as "a steroid hormone that your adrenal glands (the glands on top of your kidneys) make." It is often called the stress hormone, but that undersells how much it does. Cortisol helps regulate glucose metabolism, dampens inflammation, supports blood pressure and helps set your sleep cycle.

When something stressful happens, the body first releases fast-acting hormones like adrenaline. Cortisol follows. According to Cleveland Clinic, your body "can release cortisol after releasing its 'fight or flight' hormones, like adrenaline," which helps keep you alert and releases glucose for energy. In a hard negotiation or a product outage, that is exactly what you want.

Cortisol runs on a daily rhythm

Cortisol is not a constant. "Most people have lower cortisol levels in the evening when they go to sleep. And they have peak levels in the morning right before they wake up," Cleveland Clinic notes. The morning rise helps you get up and moving. The evening fall helps you sleep.

That rhythm is why the timing of stress matters so much for founders. A tense 9 a.m. meeting rides on top of a natural peak. A 10:45 p.m. email from a board member lands at the point your cortisol is supposed to be near its low. Repeat that often enough and the shape of the day starts to flatten: tired in the morning, wired at night.

Where did the idea of adrenal fatigue come from?

The theory sounds reasonable if you say it quickly. Stress raises cortisol. Chronic stress raises it for months or years. Eventually, the story goes, the adrenal glands tire out, cortisol falls too low, and you feel exhausted, foggy, craving salt and caffeine, and unable to recover.

The idea grew up outside mainstream endocrinology, and it is often "diagnosed" with salivary cortisol tests sold directly to consumers. The appeal is obvious. It names a real experience, promises a cause, and usually comes with a product.

Mayo Clinic's answer is direct: "Adrenal fatigue isn't an official medical diagnosis. It's a general term used to describe a group of symptoms that aren't specific." Some people believe it is a mild form of adrenal insufficiency caused by chronic stress, but, Mayo adds, "there is no evidence to support this theory."

What does the research actually show?

The most thorough look at the question is a 2016 systematic review by Flavio Cadegiani and Claudio Kater in BMC Endocrine Disorders, bluntly titled "Adrenal fatigue does not exist."

The authors screened 3,470 articles and found 58 studies that met their criteria, comparing cortisol measures in fatigued or burned-out people against healthy controls. If adrenal fatigue were real, you would expect a consistent pattern: low cortisol in the tired group. That is not what they found.

Across the three most commonly used tests, most studies found cortisol in the normal range for fatigued people. Where there were differences, they pointed in both directions, sometimes lower and sometimes higher.

The authors' conclusion leaves little room: "This systematic review proves that there is no substantiation that 'adrenal fatigue' is an actual medical condition."

They also named the weaknesses in the underlying literature: "heterogeneity of the study design," "the descriptive nature of most studies," "the poor quality assessment of fatigue," and "the use of an unsubstantiated methodology." In other words, the case for adrenal fatigue was built on inconsistent, low-quality measurement, and the better evidence does not support it.

A fair reading: a systematic review of mostly small, observational studies cannot prove a negative in an absolute sense. What it can show, and does, is that there is no consistent cortisol signature that separates tired people from healthy ones. A diagnosis that cannot be measured reliably is not a diagnosis.

Adrenal insufficiency is real, and it is different

It is important not to swing too far the other way. The adrenal glands can fail, and when they do it is serious.

Adrenal insufficiency, including Addison's disease, is a recognized condition in which the adrenals do not make enough hormones. Cleveland Clinic lists symptoms of low cortisol that include "fatigue, unintentional weight loss, loss of appetite, low blood pressure." Mayo Clinic adds body aches, nausea and salt cravings. It is diagnosed with specific blood tests and treated by physicians.

At the other end, Cushing syndrome involves too much cortisol, from causes such as high-dose steroid medications or adrenal tumors. Cleveland Clinic lists weight gain in the face and belly, muscle weakness, high blood sugar, elevated blood pressure and weak bones among its signs.

Both are real, both are testable, and both need a physician. Mayo Clinic's warning about the vague label cuts to the core risk: "accepting that symptoms are caused by a vague label, such as adrenal fatigue, could cause the true source of a problem to go without a diagnosis or treatment."

Why adrenal supplements are a real risk

The adrenal fatigue market is mostly supplements: "adrenal support," "cortisol balance," glandular extracts. Supplements in the US are not approved by the FDA for safety or effectiveness before they are sold, and quality varies.

That matters here in a specific way. Research published in Mayo Clinic Proceedings, as reported by Bioscientifica, found that "many dietary supplements claiming to be energy boosters for adrenal fatigue contain thyroid hormones and steroids not listed on the label, and therefore have potentially dangerous side effects."

Think about what that means for a tired founder. You take a product because a salivary test told you your cortisol was off. It contains undeclared thyroid hormone or steroids. You might feel a lift. You might also be suppressing your own adrenal function, straining your heart or masking the real cause of the fatigue. If you are taking any adrenal or cortisol product now, tell your physician before you stop or continue it, because stopping steroid-containing products abruptly can itself be risky.

What the evidence says, and what it doesn't

Well established: Cortisol is central to the stress response and runs on a daily rhythm. Adrenal insufficiency and Cushing syndrome are real conditions diagnosed with validated tests.

Well supported: Adrenal fatigue is not a recognized diagnosis. A systematic review of 58 studies found no consistent cortisol pattern in fatigued people, and major medical centers do not accept it.

Also supported, and more useful: Chronic stress does change the body. The concept of allostatic load describes how a stress response that never switches off affects sleep, blood pressure, glucose and inflammation. We cover it in what chronic stress does to a founder's body. The problem is real; it just is not "burned-out adrenals."

Not supported: That consumer saliva tests can diagnose an adrenal problem, or that supplements "restore" adrenal function.

What an exhausted founder can actually do this week

If you are tired all the time, the first move is to treat that as a real symptom with real possible causes, and to get those checked.

Book a physician visit and describe the fatigue plainly. How long, how bad, what time of day, what else has changed. Common medical causes of fatigue include sleep apnea, anemia, thyroid problems, depression, diabetes and medication side effects. If adrenal insufficiency is a genuine possibility, your physician can test for it properly. That one appointment is worth more than any supplement.

Look hard at sleep. For many founders, the real explanation for afternoon crashes is five and a half hours a night plus late screens. A fixed wake time, a real wind-down and no work in bed are unglamorous and effective. Meditation for sleep for executives lays out a routine.

Respect the cortisol curve. Put light and movement in the first hour of the day, when cortisol naturally peaks. Protect the last hour before bed from email and hard conversations, when it should be falling. Move caffeine earlier.

Check the load, not just the glands. Ask whether the fatigue started with a specific stretch: a fundraise, a layoff, a co-founder split, or the strange emptiness after an exit that we explore in meditation after an exit. Often the body is responding appropriately to an inappropriate load.

Skip the saliva test and the adrenal supplements. Put the money and attention toward sleep, a doctor's visit and one daily downshift practice.

Training the off switch

The adrenal fatigue story gets one thing right: the stress response is supposed to switch off, and for a lot of founders it does not. That is a trainable problem. Slow breathing, meditation and deliberate recovery help the nervous system return to baseline faster after each spike, which over time is what lowers the load.

That is what we work on at Cinder, in private 1:1 coaching built around the rhythm of an operator's week. No supplements, no tests to sell, just a steadier nervous system and better recovery between demanding days.

A better question than "are my adrenals tired?"

A more useful question is: what is my body responding to, and what would help it recover? If you want help answering that and building a practice that holds up under real pressure, we would like to hear from you.

Apply for private coaching

Sources

• Cortisol: what it is, function, symptoms and levels, Cleveland Clinic, 2025
• Adrenal fatigue: What causes it?, Mayo Clinic, 2024
• Adrenal fatigue does not exist: a systematic review, BMC Endocrine Disorders, 2016
• Adrenal fatigue dietary supplements unsafe, Bioscientifica (Mayo Clinic Proceedings study), 2018