ACTH vs cortisol: how the two hormones work together

ACTH and cortisol are two links in one chain. ACTH is the signal, and cortisol is the response. The brain sends the signal, the adrenal glands answer, and the answer feeds back to turn the signal down. That is why the two are usually measured together, and why neither makes much sense alone.

This page explains how the chain works. It doesn’t map pairs of results to conditions. How a clinician reads a particular pair depends on the time of the draw, your medicines, your symptoms and further tests, so that part belongs in the appointment.

ACTH

One blood test for ACTH, the hormone that tells the adrenal glands to make cortisol.

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The chain, step by step

Three hormones make up the loop. You will see CRH named in some searches and in clinic tests, even though it isn’t something most people have measured.

Hormone	Made in	What it does
CRH (corticotropin-releasing hormone)	The hypothalamus, part of the brain	Tells the pituitary gland to make ACTH
ACTH (adrenocorticotropic hormone)	The pituitary gland	Tells the adrenal glands to make cortisol
Cortisol	The adrenal glands, two small glands above the kidneys	Acts across the body, and signals back to the hypothalamus

NIDDK describes it in that order: CRH tells the pituitary to make ACTH, which in turn tells the adrenals to make cortisol. When cortisol rises enough, it turns off the CRH signal, so ACTH and cortisol fall.

That last step is what makes it a loop. MedlinePlus puts it this way: normally, if cortisol drops too low, ACTH rises to trigger the adrenal glands, and if cortisol is high, ACTH decreases so the adrenal glands make less.

Does ACTH stimulate cortisol?

Yes. ACTH is the hormone that stimulates the adrenal glands to make cortisol. That is the basis of the ACTH stimulation test, where a clinician gives a dose of man-made ACTH and measures how much cortisol follows. See below.

CRH vs ACTH

They are different hormones from different glands, one step apart. CRH comes first, from the hypothalamus, and acts on the pituitary. ACTH comes second, from the pituitary, and acts on the adrenal glands. CRH release follows a daily cycle, according to a medical-education review, and may also be released in response to stress and low blood sugar.

Rising together through the day, pushing against each other in the loop

This trips people up. Two things are true at once.

• Through the day, they rise and fall together. A medical-education review says ACTH and cortisol both peak in the morning and are lowest in the late evening. The daily CRH cycle sets this pattern.
• Through the feedback loop, they push against each other. When cortisol is higher than the body wants, ACTH is turned down. When it is lower, ACTH is turned up.

So a clinician can’t read either number without the time of day and the other number beside it.

Why clinicians measure both

MedlinePlus says ACTH testing is usually done with a blood test for cortisol, because ACTH controls how much cortisol you make. Conditions that affect any part of the system, from the hypothalamus to the pituitary to the adrenal glands, can change the amount of cortisol in your body. ACTH and cortisol tests are used together to help find out which type of condition may be behind an abnormal cortisol level.

Put plainly, the pair helps a clinician decide where in the loop to look. It doesn’t answer that on its own. MedlinePlus says other tests are often needed to make a final diagnosis, and that your provider will usually compare your ACTH level with your cortisol level.

How clinics test the loop

A single blood draw shows where the loop is at one moment, and one cortisol or ACTH result can’t diagnose or rule out Cushing’s syndrome or adrenal insufficiency. To see how it responds, clinicians sometimes push it and measure what follows. NIDDK describes these tests. They are done in clinics, arranged by a clinician, and are not something to try yourself.

• ACTH stimulation test. You get an injection of man-made ACTH. Blood is drawn before and 30 or 60 minutes after, and cortisol is measured. It checks whether the adrenal glands respond to the signal.
• CRH stimulation test. You get an injection of CRH. Blood is drawn before and over the next two hours, and ACTH is measured. It checks how the pituitary responds to the signal above it.
• Dexamethasone suppression test. You take dexamethasone, a type of glucocorticoid, usually around 11 p.m. Blood is drawn the next morning, around 8 a.m. It tests whether the feedback that turns cortisol down is working.

How to read the results of these tests is for the clinician, and it depends on the test and your situation.

Medicines that act on the loop

Steroid medicines act on this same system. NIDDK says high steroid levels over a long time make the hypothalamus produce less CRH, which means less ACTH, and that the most common cause of adrenal insufficiency overall is suddenly stopping corticosteroids after taking them for a long time. So tell any clinician reading your ACTH and cortisol that you take, or recently took, a steroid in any form. Never stop or change a steroid medicine yourself. Ask your prescriber.

Ordering the pair

The seller lists ACTH and a cortisol with a morning sample as separate orders. Both pages leave details open, so check the timing on each order before you buy. The seller’s cortisol AM and PM page gives a morning window and a later one but is unclear about the second draw, and its ACTH page gives no draw-time instructions. Follow the instructions on your lab order, and ask the lab if the two can be drawn in the same visit.

Ordering both doesn’t replace the clinician who reads them together. Prices for the same type of test vary widely between sellers, and it is worth comparing. See cost and where to buy.

• CortisolOne cortisol result. Check what time of day the order asks for $109 See this test at HealthLabs

Sold by HealthLabs. Prices checked November 2026. Not available in ND, RI, NY, NJ, MD and HI. We earn a commission on sales.

When to see a clinician

If you have symptoms that could come from too much or too little cortisol, see a clinician. If you have repeated vomiting, severe weakness or fainting, don’t wait for a test. Call 911 or go to the nearest emergency room. See adrenal crisis.

Keep reading

• ACTH blood test

  What the test measures and how to prepare.

• ACTH levels

  The daily rhythm and why one number needs context.

• AM and PM timing

  When cortisol samples are taken and why.

• The HPA axis

  The same loop, in more detail.