Low cortisol symptoms: signs of adrenal insufficiency and when to get help

Low cortisol, known medically as adrenal insufficiency, causes extreme tiredness, loss of appetite and weight loss, feeling sick, dizziness when you stand up, salt craving and, in some people, patches of darker skin.¹ Cortisol helps keep up blood pressure, blood sugar and energy, so too little of it leads to fatigue, low blood pressure and weight loss.² It has three main causes: damage to the adrenal glands themselves (Addison's disease), a pituitary problem that leaves the adrenal glands without their signal, and long-term steroid medicine, particularly when it is stopped suddenly.³⁴ Low cortisol can turn into a life-threatening adrenal crisis, so it is diagnosed and treated by doctors, with blood tests, not with a home test.

What are the symptoms of low cortisol?

The NHS lists these as the main symptoms of Addison's disease, the most familiar form of low cortisol:¹

• extreme tiredness
• patches of darker skin
• loss of appetite, weight loss and tummy pain
• feeling sick
• craving salty food
• feeling dizzy when you stand up
• joint pain, muscle weakness and cramps
• feeling thirsty and peeing a lot
• anxiety and depression

Darker skin is a feature of primary adrenal insufficiency only, where the adrenal glands themselves are damaged. It does not happen when the problem starts in the pituitary gland.⁵

Many of these symptoms are vague and common. Tiredness, low mood and dizziness have many causes, and the Endocrine Society points out that people with symptoms often put down to "adrenal fatigue" may in fact have adrenal insufficiency, depression, obstructive sleep apnoea or another condition.⁶ That is why persistent symptoms need a doctor's assessment rather than a guess. If you have the opposite pattern, such as weight gain around the middle and easy bruising, see high cortisol symptoms.

What causes low cortisol?

Cortisol is made in the adrenal cortex, the outer layer of the adrenal glands.² The pituitary gland in the brain controls how much is made by releasing a hormone called ACTH, which tells the adrenal glands how much cortisol to produce.³ Low cortisol can start at either end of that chain.

• Addison's disease (primary adrenal insufficiency). The adrenal cortex is damaged. In Western countries about 90 per cent of cases are autoimmune, meaning the immune system attacks the glands.⁷ Infections such as tuberculosis are another cause.³ Addison's disease is rare: about 9,000 people in the UK have the diagnosis, and about 320 are diagnosed each year.⁷
• Secondary adrenal insufficiency. The adrenal glands are healthy but are not told to make cortisol, because of a pituitary problem, a brain injury, surgery to the pituitary or an autoimmune condition.³
• Steroid medicines. The most common cause of abnormal cortisol levels, covered in the next section.³

Our guide to testing for Addison's disease covers that condition in more depth.

Steroid medicines and low cortisol

Steroid medicines such as prednisolone act like cortisol. Taken for a long time, they lead the body to turn down its own production, and when the medicine is stopped or reduced the adrenal glands may not pick up again straight away. This is called glucocorticoid-induced adrenal insufficiency, and at least 1 per cent of the population is at risk of it because they take steroids long term.⁴ MedlinePlus lists taking steroid medicines for a long time, or suddenly stopping them, as the most common cause of abnormal cortisol levels.³

It is not only tablets. NICE notes that people using inhaled, injected or skin steroids at doses equal to or above the body's natural output may have a low morning cortisol.⁵

If you take steroids, do not stop them or lower the dose suddenly without talking to the doctor who prescribes them, and tell any doctor treating you that you take them. If you have been on steroids and develop the symptoms above, especially during another illness, get medical advice promptly.

Adrenal crisis: when to call 999

An adrenal crisis is a sudden, severe shortage of cortisol and a medical emergency. The NHS advises calling 999 if someone with Addison's disease suddenly gets worse or has any of these:¹

• a fast heart rate
• severe dizziness, especially when standing up
• severe pain in the tummy or side
• muscle weakness, pain or spasms
• a headache that does not go away
• feeling or being sick
• drowsiness, irritability or confusion
• a seizure, or loss of consciousness

In the US, call 911. If the person carries an emergency hydrocortisone injection it should be given, but call 999 even after it has been given.¹ In hospital, emergency treatment is an immediate 100 mg injection of hydrocortisone followed by 200 mg over the next 24 hours, with fluids to rehydrate.⁸

A crisis is not always obvious, and it is not limited to people already diagnosed. NICE advises doctors to suspect it in anyone critically unwell with low blood pressure, low sodium, low blood sugar, shock or collapse, or an illness that is not responding to treatment, and to consider it in people at risk who have milder symptoms such as lethargy, clamminess, feeling cold or feverish, confusion or weakness.⁵

People known to have adrenal insufficiency follow "sick day rules" to prevent a crisis. During an illness with a fever that needs bed rest or antibiotics, the usual daily dose of tablets is doubled, and during prolonged vomiting or diarrhoea the steroid is given by injection instead.⁸ Your endocrine team will give you your own plan.

How low cortisol is diagnosed

The first test is usually a blood sample taken between 8 and 9am, close to the time cortisol normally peaks.⁵⁹ For people aged 16 and over, NICE uses these thresholds, which apply to modern laboratory methods (immunoassays):⁵

• below 150 nmol/L: adrenal insufficiency is possible, and the person should be referred to an endocrinologist
• 150 to 300 nmol/L: uncertain, and the test may be repeated
• above 300 nmol/L: adrenal insufficiency is very unlikely

If your result is in µg/dL, our cortisol converter changes the units. Timing and medicines matter: one NHS laboratory states that a cortisol taken at a random time, or while on steroid treatment, cannot be interpreted.¹⁰ Oral oestrogen, found in many contraceptive pills and some HRT, makes blood cortisol read falsely high, so NICE advises stopping it for 6 weeks before the test; your doctor will tell you whether that applies to you.⁵

If the morning result is low or uncertain, the diagnosis is confirmed in hospital with a Synacthen test (also called an ACTH stimulation test). Blood cortisol is measured before and 30 or 60 minutes after an injection of 250 µg of tetracosactide, a synthetic version of ACTH. With healthy adrenal glands cortisol rises above about 500 to 550 nmol/L, and a peak below 500 nmol/L points to adrenal insufficiency, although the exact cut-off depends on the laboratory's method.⁷ The Endocrine Society calls the short Synacthen test the gold-standard test for primary adrenal insufficiency.¹¹ See the Synacthen test for what to expect on the day.

Hair cortisol has no role here. Neither the Endocrine Society guideline nor NICE includes it, and the Synacthen test remains the standard.¹¹⁵ A hair test also looks backwards: the hair nearest the scalp reflects cortisol from roughly 1.3 to 2.2 months before it was cut, so it cannot show whether someone is short of cortisol today.¹² No home test can diagnose or rule out adrenal insufficiency.

Is it low cortisol or "adrenal fatigue"?

"Adrenal fatigue" is a popular idea that everyday stress wears out the adrenal glands and causes tiredness. The Endocrine Society says there is no scientific proof that it is a real medical condition, and that no test can detect it.⁶ A systematic review found 58 relevant studies among 3,470 articles, with results that conflicted almost systematically, and concluded there is no evidence that adrenal fatigue exists.¹³

Adrenal insufficiency is different: a measurable shortage of cortisol, diagnosed with blood tests and treated with replacement steroid medicine, which doctors adjust mainly by watching symptoms, weight, energy levels and blood pressure.¹¹ If you are exhausted, see a GP rather than relying on a test or supplement sold for adrenal fatigue. Our guide to adrenal fatigue looks at the claims in more detail.