Low cortisol: what it means and what to do

A low cortisol is often down to a test taken late in the day or to steroid medicines. Sometimes, though, it means the adrenal glands make too little. That is rare, but it needs looking at soon, because your body needs cortisol to cope with illness or strain.

What low cortisol means

Cortisol is lower in the evening and at night. A low result only carries weight if the blood was taken early in the morning.

In the morning, a cortisol below 5 µg/dL, read together with ACTH, points to adrenal insufficiency. To confirm it, doctors use a stimulation test: a hormone similar to ACTH is injected and cortisol is measured after 30 and 60 minutes. If the peak stays below 18 µg/dL, the adrenal glands respond poorly (the exact limit depends on the method).

If the adrenal glands are damaged, ACTH is high. If the problem starts in the pituitary, ACTH is low or normal.

What causes low cortisol

The first two are by far the most common.

• A test taken late in the day: Cortisol is normally lower in the afternoon. It should be repeated early in the morning.
• Steroid medicines: Tablets, inhalers, creams or joint injections hold back your adrenal glands. After long use, stopping suddenly can be dangerous.
• Pituitary problems: If the pituitary makes too little ACTH, the adrenal glands are not stimulated. This can follow surgery, an injury or a benign tumour.
• Addison’s disease: The immune system damages the adrenal glands. It is rare, and often goes with other autoimmune conditions, such as thyroid disease.
• Other medicines and conditions: Some medicines, severe infections or bleeding into the adrenal glands can lower it. Your doctor looks at each case.

Symptoms of low cortisol

When the adrenal glands make too little cortisol, symptoms come on slowly and are vague. For example:

• Tiredness that does not go away, and weakness
• Weight loss and a poor appetite
• Nausea, sometimes tummy pain
• Dizziness when you stand up, from low blood pressure
• Craving salty food, and in Addison’s darker skin

An illness, flu or surgery can make everything worse within hours. This is an adrenal crisis, and it is an emergency.

Low cortisol and adrenal fatigue

Online you will read about ‘adrenal fatigue’: adrenal glands worn out by stress, making less cortisol. It is not a recognised diagnosis, and studies have not found it.

Real adrenal insufficiency does exist, but it is something else: it shows up on specific tests and is treated with replacement therapy. Adrenal supplements do not help and can contain hormones. Ask your doctor.

Which tests to read alongside it

These tests help show whether the adrenal glands really make too little.

What to do if your cortisol is low

Where to start:

• Check the time of the test: if it was in the afternoon, the result may be normal for that hour.
• Tell your doctor about every steroid medicine you use or used in the past year, including inhalers, creams and joint injections.
• If your doctor suspects insufficiency, they order ACTH and a stimulation test, often with an endocrinologist.
• If you have been diagnosed and take treatment, your doctor explains how to raise the dose when you are ill. Carry your steroid card.

Do not stop or change your steroids on your own: after long use they must be tapered with your doctor.

Low cortisol: when to worry

Talk to your doctor if:

• Your morning cortisol is below the limit on your report.
• You have been tired for weeks, are losing weight, feel dizzy when you stand or crave salt.
• You recently stopped a steroid you took for a long time and feel very weak.
• You have extreme weakness, vomiting that will not stop, severe tummy pain, fainting or confusion: call 112 or go to the emergency department. If you take treatment for your adrenal glands, say so straight away.

Frequently asked questions

What are the symptoms of low cortisol? Tiredness that does not go away, weight loss, nausea, dizziness when you stand, craving salt. Extreme weakness with vomiting or fainting is an emergency: call 112.

When should I worry about low cortisol? When it is low in a morning test, especially with tiredness, weight loss or low blood pressure. A low result in the afternoon is usually normal for the time of day.

Do steroid medicines lower cortisol? Yes. Steroid medicines, including inhalers and creams, hold back your adrenal glands. That is why, after long use, steroids are tapered with your doctor and never stopped suddenly.

How do I raise my cortisol? If it is low because of the time of the test, there is nothing to raise. If there is real insufficiency, it is treated with replacement therapy prescribed by your doctor. Supplements do not replace it.

Is low cortisol linked to tiredness? In adrenal insufficiency, yes. But tiredness has many more common causes, such as anaemia, thyroid, sleep or mood. Your doctor looks at the whole picture.

Does Rosa test cortisol? No. Rosa measures sodium, potassium, blood sugar and TSH, which help read a low cortisol. If your doctor wants cortisol, they order it separately.

Sources

• Bornstein and colleagues, diagnosis and treatment of primary adrenal insufficiency: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism, 2016. PMID 26760044
• Nieman and colleagues, the diagnosis of Cushing’s syndrome: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism, 2008. PMID 18334580
• Cadegiani and Kater, adrenal fatigue does not exist: a systematic review. BMC Endocrine Disorders, 2016. PMID 27557747
• Fondazione Policlinico Universitario A. Gemelli IRCCS, clinical chemistry laboratory: list of tests and reference intervals, 2024. Policlinico Gemelli, elenco prestazioni CDS.002