Prednisone and cortisol: how steroid medicines change cortisol results

Prednisone is a steroid medicine. It isn’t cortisol, but it acts like cortisol in the body. Taken for a long time, it can lower the cortisol your own adrenal glands make. It can also change a cortisol blood test, in either direction, depending on how the lab measures. This page explains how, and also covers hydrocortisone and dexamethasone.

One rule applies to everything below. Don’t stop, skip or change a prednisone dose, or any steroid, because of a cortisol test or something you read here. Ask the prescriber. Stopping suddenly after long-term use is the most common cause of adrenal insufficiency, according to NIDDK.

Does prednisone increase cortisol?

Not the cortisol your body makes. The answer depends on what you mean by cortisol.

In the body, prednisone acts like cortisol. NIDDK calls medicines of this type glucocorticoids, “similar to cortisol”, and says more than 10 million Americans take them each year. MedlinePlus lists taking large doses of steroid medicines such as prednisone for a long time as a cause of high cortisol levels and Cushing syndrome.

At the same time, the medicine tells the brain to stand down. NIDDK describes it this way: prescription doses can put more steroid in the blood than the body normally makes. After a long time, the hypothalamus makes less of its signal, the pituitary makes less ACTH, and the adrenal glands stop making cortisol. So the medicine adds steroid effect while the body’s own cortisol falls. See the HPA axis for the chain.

What a blood test shows then depends on the method, as the next section explains.

Steroids other than pills

NIDDK says steroids are also injected into joints to treat pain, and used after organ transplants to suppress the immune system. A 2024 review says steroids in inhalers or creams could suppress your own cortisol as well. In a clinical example it cites, a significant share of people using inhaled steroids had low cortisol levels, although their steroid exposure meant their overall glucocorticoid status could still be high.

A 2023 laboratory review also notes that potent steroids have been found hidden in some cosmetics and herbal creams. If a product is on your skin or in your supplement drawer, say so.

What steroids do to a cortisol blood test

Three things can matter.

Your own cortisol is suppressed. After long-term treatment, a blood cortisol can come back low because the body has dialed down production. A low result in someone taking steroids is not the same finding as a low result in someone who isn’t. MedlinePlus says the most common cause of abnormal cortisol levels is taking steroid medicines for a long time or suddenly stopping them.

The test can read the medicine as cortisol. A 2024 review says direct cortisol immunoassays can cross-react with prednisolone, a related steroid medicine. A 2023 review lists synthetic glucocorticoids as a cause of false results in immunoassays. Mass spectrometry separates compounds before measuring them, and the 2023 review says it can be designed to avoid interference from prednisolone. That review cites a laboratory that found detectable prednisolone in a third of cortisol samples in the first year it used a mass spectrometry method. So the same blood could read differently on two methods, which is a reason to ask which method your lab uses.

Published cut-offs may not apply. The 2026 study of morning cortisol thresholds left out people on chronic glucocorticoid therapy, so its cut-offs weren’t tested in this group.

Because of all this, a clinician decides whether and when to test, and which test, if you take steroids. A single blood cortisol can’t diagnose or rule out adrenal insufficiency or Cushing’s syndrome, and it is even less clear on a steroid.

What to tell the person who orders or runs the test

MedlinePlus advises letting your provider know about all the medicines you use, including skin creams, and not stopping any medicine without talking to your provider first. For a cortisol test, that means telling them about:

• Steroid pills, such as prednisone, prednisolone or dexamethasone.
• Hydrocortisone in any form, including tablets and creams.
• Steroid inhalers, nasal sprays, eye drops and injections.
• Creams, herbal products and supplements you use.
• The date of your last dose and any recent change made by your prescriber.

Hydrocortisone and cortisol

Hydrocortisone is cortisol made as a medicine. A 2021 review calls it the synthetic form of cortisol. NIDDK says that when the adrenal glands don’t make enough cortisol, it is replaced with a corticosteroid, most often hydrocortisone, and that prednisone or dexamethasone are used less often.

Two points follow:

• Hydrocortisone cream on your hands can contaminate a saliva sample and raise the result, and so can oral hydrocortisone. The 2023 review notes this for saliva tests, and says that a cortisol-to-cortisone ratio can help spot it.
• Cortisone is a different, inactive compound. See cortisol vs cortisone vs hydrocortisone.

Is cortisol itself a steroid? Yes. It is a steroid hormone made by the adrenal glands, and the 2023 adrenal insufficiency review lists it alongside aldosterone as one. “Steroid medicine” on this page means a corticosteroid such as prednisone, not the muscle-building kind.

Dexamethasone and the dexamethasone suppression test

Dexamethasone is a glucocorticoid. It is sometimes used as a treatment. It is also used as a test, run by a clinician, to look for too much cortisol.

NIDDK describes the low-dose version. You take dexamethasone around 11 p.m., and blood is drawn the next morning around 8 a.m. A variation uses doses every 6 hours for 48 hours. Normally cortisol drops after dexamethasone. A level that doesn’t drop suggests Cushing’s syndrome. NIDDK says no one test is perfect, so doctors usually do two tests to confirm a diagnosis.

A 2023 review adds that:

• Cut-offs have to suit the local cortisol method.
• Some medicines change how fast the body clears dexamethasone, so they can cause false results.
• Oral estrogens raise carrier proteins and can affect the result. See birth control and cortisol.
• The overnight test is not the first choice in pregnancy.
• A longer, two-day version may be preferable in women taking the pill.

Dexamethasone tests belong with a clinician. They aren’t a home test or something to order yourself.

What does a cortisol of 0.9 after dexamethasone mean?

We can’t interpret an individual number, and a bare number can’t be read. The unit matters: micrograms per deciliter and nanomoles per liter differ many times over, and our cortisol units converter shows how. The cut-off also depends on the lab’s method and on the clinical question. Take the result back to the clinician who ordered the test.

If you take steroids and become unwell

NIDDK says a severe infection, severe diarrhea, or vomiting that stops you keeping steroid pills down needs immediate medical attention, in an emergency room if necessary, because it can lead to an adrenal crisis. Call 911 or go to the nearest emergency room. See adrenal crisis.

For anything less urgent, such as symptoms that worry you while on a steroid, call your prescriber. Coming off a steroid is a prescriber matter too. NIDDK says doctors lower the dose gradually over weeks or even months and watch for symptoms. See causes of low cortisol.

If you are thinking about ordering a test

If you take a steroid, speak to your prescriber first. A cortisol blood test on a steroid may be hard to read, as above. If you take a medicine that can’t be stopped, a 2023 review says to discuss it with the laboratory. If you have stopped a steroid under medical supervision and want a baseline for a clinician, the test can be a starting point for that conversation, but it won’t confirm recovery. Follow the draw time and fasting instructions on your lab order. Don’t stop or change a medicine for a test.