Cortisol spike: what it means and what it doesn't

A cortisol spike is a short rise in cortisol, usually after something stressful or physically demanding. It is a normal part of how the body handles a challenge, and it happens many times in a normal day.

The term has taken on a bigger meaning online, where a “spike” is blamed for how people feel. This page covers what a spike is, what sets one off, what a test can and can’t show, and what a “crash” isn’t.

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A blood test is a snapshot and can't capture a spike that comes and goes. A morning and later pair shows how cortisol changes across one day. A single blood cortisol can't diagnose or rule out Cushing's syndrome.

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What is a cortisol spike?

Cortisol is made by the adrenal glands, and MedlinePlus says it helps your body respond to stress. When the brain senses a challenge, it triggers a chain: the hypothalamus releases CRH, the pituitary releases ACTH, and ACTH tells the adrenal glands to release cortisol. A review in Frontiers in Endocrinology describes this chain and says the fast “fight or flight” response, which involves adrenaline, comes first and leads to activation of the cortisol system. The cortisol itself then feeds back and turns the signal down.

That is a spike: cortisol rising in response and then falling back. The same review says an acute stressor, such as a near-miss in traffic, triggers an immediate response that usually subsides shortly after the stressor ends.

MedlinePlus puts it this way: not all stress is bad, and a little short-term stress can sometimes be helpful. A spike is not a malfunction.

What causes cortisol spikes?

Many ordinary things raise cortisol for a while.

• Stress. MedlinePlus says stress and exercise can raise cortisol levels, as can hot and cold temperatures.
• Illness, surgery or pain. A primary care review lists physical stress such as hospitalization, surgery and pain among the situations that raise cortisol.
• Changes to the sleep-wake cycle. Endocrine Reviews says shift work and jet lag activate the stress-hormone system and change the normal pattern.
• The body’s own pulses. Endocrine Reviews says cortisol is released in pulses every 1 to 2 hours, on top of the daily rhythm. A reading is therefore a point on a moving line, not a fixed level.
• Medicines. Steroid medicines such as prednisone act like cortisol in the body, and some can change cortisol test results. See causes of high cortisol.

Cortisol also reaches its daily peak in the morning, which isn’t a spike in this sense. See high cortisol in the morning.

What does a cortisol spike feel like?

Nothing specific. The sources we checked don’t link any single feeling to a cortisol rise on its own.

MedlinePlus describes the general stress response: hormones are released that make you alert and ready to act, and raise blood pressure, heart rate and blood glucose. It doesn’t name cortisol as the cause of any one of these. The Frontiers review points out that adrenaline-type hormones act before the cortisol rise begins. So a racing heart, a jolt or a wired feeling may come from the fast part of the response rather than from cortisol itself. See cortisol versus adrenaline.

Some lists online attach anxiety or poor sleep to a “cortisol spike”. The sources we checked don’t back a symptom list for a spike. If a symptom is persistent, treat it as a symptom and take it to a clinician rather than assuming a cause.

Does a cortisol spike raise blood sugar?

Short-term, the stress response does. MedlinePlus says stress hormones raise blood glucose. A review of glucocorticoids and insulin resistance says acute glucocorticoid release mobilizes energy for fight or flight, while long-term exposure from drug treatment or Cushing’s syndrome progressively leads to insulin resistance. That evidence is for glucocorticoid excess. It is not for the spikes of an ordinary day.

What a cortisol crash is not

“Cortisol crash” and “cortisol drop” are popular phrases for the tired feeling after a stressful stretch. They aren’t medical terms. After a stressor ends, cortisol comes back down on its own, which is the normal feedback loop.

Tiredness has many causes. The sources are clear on one idea sometimes attached to it. Adrenal fatigue, the idea that the adrenal glands wear out from stress, is not a recognized diagnosis. A 2016 systematic review found no support for it as a medical condition, and a 2024 paper in the Journal of the Endocrine Society says it has never been scientifically proven to exist. Truly low cortisol is a different condition, adrenal insufficiency, with its own signs. See low cortisol and adrenal fatigue.

Can a test show a cortisol spike?

Not reliably. A blood cortisol is one sample at one moment.

• Stress and exercise can raise cortisol, and MedlinePlus says you may need to rest before a blood test.
• Cortisol pulses and follows a daily rhythm, so the same person has different values an hour apart.
• Endocrine Reviews says single values don’t necessarily reflect a person’s glucocorticoid status, because of this variation.

Doctors look for different things. A lab review in Diagnostics says Cushing’s syndrome can show up as a loss of the night-time dip, which is why a late-night saliva test is used. That is a flat pattern, not a spike. The primary care review adds that a random cortisol is unreliable for screening. NIDDK says doctors usually do two tests, such as a 24-hour urine test, a late-night saliva test or a dexamethasone suppression test.

A morning and later blood pair shows how cortisol changes across one day. It won’t tell you what happened during a stressful afternoon. For devices that claim to track cortisol, see wearables and cortisol. For the clinic tests, see testing for high cortisol.

When a spike isn’t just a spike

Brief rises are normal. Take it to a clinician if you have several of the specific signs of long-term cortisol excess, such as easy bruising, wide purple stretch marks or muscle weakness. The full list is in the guide to high cortisol symptoms.

If you take a steroid medicine, don’t stop or change it because of anything you read here. Ask the prescriber.

Questions people ask

What does a cortisol spike mean?

Usually that your body reacted to something: stress, exercise, illness, temperature or a change in sleep. The reaction is normal and temporary.

Are cortisol spikes dangerous?

MedlinePlus says short-term stress responses can be helpful. The harm described in the sources comes from long-term excess, such as Cushing’s syndrome. See what high cortisol does to your body.

What causes cortisol spikes at night?

Cortisol normally rises from the early hours of the night, as covered on the morning page. It is normally lowest around midnight. A feeling of being awake at night can’t be read as a cortisol level.

Keep reading

• High cortisol symptoms

  The signs doctors link to too much cortisol.

• High cortisol in the morning

  The normal peak and the early-hours rise.

• Cortisol versus adrenaline

  Which hormone does what in the stress response.

• Cortisol and wearables

  What devices can and can't tell you.

• Testing for high cortisol

  Which test answers which question.