Low cortisol means your body isn’t producing enough of the hormone it needs to regulate blood pressure, blood sugar, energy, and your response to stress. A normal morning cortisol level falls between 10 and 20 micrograms per deciliter, and levels consistently below that range point to a condition called adrenal insufficiency. The causes range from autoimmune disease to medication withdrawal, and the symptoms can be vague enough to go undiagnosed for months or years.
What Cortisol Does in Your Body
Cortisol is often called the “stress hormone,” but that label undersells it. Your body uses cortisol around the clock to keep blood sugar stable between meals, maintain blood pressure, control inflammation, and break down fats and proteins for energy. It follows a daily rhythm, peaking in the early morning to help you wake up and dropping to its lowest point around midnight.
Production is controlled by a chain reaction between three parts of your body. A region in the brain called the hypothalamus sends a signal to the pituitary gland (a pea-sized structure at the base of the brain), which then tells the adrenal glands, sitting on top of your kidneys, to release cortisol. When cortisol levels rise high enough, the brain dials back its signals. This feedback loop keeps levels in a tight range. Low cortisol results when any link in that chain breaks down.
Why Cortisol Drops: Three Categories
Damage to the Adrenal Glands (Primary)
When the adrenal glands themselves are damaged and can no longer make cortisol, it’s called primary adrenal insufficiency, or Addison’s disease. The most common cause is an autoimmune reaction where the immune system attacks the adrenal cortex, the outer layer of the gland responsible for hormone production. Infections, bleeding into the adrenal glands, and certain medications can also destroy adrenal tissue. People with one autoimmune condition are at higher risk for developing others, so Addison’s disease frequently appears alongside thyroid disease, type 1 diabetes, or celiac disease.
Problems With the Pituitary Gland (Secondary)
The adrenal glands may be perfectly healthy but receive no signal to produce cortisol. This happens when the pituitary gland is damaged by a tumor, infection, surgery, bleeding, or traumatic brain injury. Without the pituitary’s messenger hormone reaching the adrenals, cortisol production stalls. The adrenal glands essentially sit idle.
Stopping Steroid Medications Too Quickly (Tertiary)
This is the most common cause of low cortisol overall. Taking prescription corticosteroids (for conditions like asthma, rheumatoid arthritis, or inflammatory bowel disease) floods the body with synthetic cortisol. The brain responds by turning down its own signaling, and the adrenal glands gradually shrink from disuse. If you’ve taken a dose equivalent to 5 mg of prednisone daily for three weeks or longer, your adrenal glands may no longer be capable of producing cortisol on their own.
Stopping suddenly leaves the body with no cortisol supply at all, neither external nor internal. Recovery generally takes about one month for every month of suppression, and can stretch to 9 to 12 months when steroids were used for over a year. This is why doctors taper steroid doses gradually, reducing by small amounts over weeks or months to give the adrenal glands time to wake back up.
What Low Cortisol Feels Like
The symptoms develop gradually and are easy to attribute to other things. Chronic fatigue that doesn’t improve with rest is typically the first sign. You may lose your appetite and lose weight without trying. Blood pressure drops, causing dizziness when you stand up. Many people develop nausea, vomiting, diarrhea, or abdominal pain that seems to come and go without explanation. A strong craving for salty foods is common because low cortisol disrupts the body’s ability to retain sodium.
Mood changes are frequent. Depression, irritability, decreased motivation, and difficulty concentrating can all stem from inadequate cortisol. These psychiatric symptoms often lead people to seek help from a mental health provider before the hormonal cause is identified.
One symptom is distinctive to primary adrenal insufficiency: darkening of the skin. When the adrenal glands fail, the brain ramps up its signaling hormone in an attempt to force them to work. That same hormone stimulates pigment-producing cells in the skin, causing a bronzing effect that’s most visible on sun-exposed areas, elbows, knees, knuckles, gums, and the creases of your palms. This hyperpigmentation does not occur in secondary or tertiary insufficiency because the brain’s signaling is the problem, not the adrenal glands.
Adrenal Crisis: The Emergency
Low cortisol becomes dangerous when the body faces a stressor it can’t match with an adequate cortisol response. An infection, surgery, severe injury, or even a stomach virus can tip someone with adrenal insufficiency into an adrenal crisis. Blood pressure plummets (systolic pressure below 100 mmHg or dropping 20 points below your usual baseline), confusion sets in, and without treatment, the situation can progress to shock, coma, and death. Fever can spike as high as 105°F.
The early warning signs overlap with many common illnesses: nausea, vomiting, severe abdominal pain, weakness, and dizziness. What separates a crisis from an ordinary stomach bug is that the symptoms escalate rapidly and don’t respond to fluids or rest. Emergency treatment with injectable hydrocortisone and intravenous fluids typically produces noticeable improvement within one to two hours. People diagnosed with adrenal insufficiency usually carry an emergency injection kit and wear medical alert identification for this reason.
How Low Cortisol Is Diagnosed
A morning blood draw is the starting point. Cortisol levels between 6 and 8 a.m. should fall in the 10 to 20 mcg/dL range. A level well below that range raises suspicion, but a single blood test isn’t always enough because cortisol fluctuates throughout the day.
The gold standard test is the ACTH stimulation test. You receive an injection of synthetic ACTH, the hormone that normally tells your adrenal glands to produce cortisol, and your blood is drawn at baseline, 30 minutes, and 60 minutes afterward. Healthy adrenal glands respond by raising cortisol above a certain threshold (roughly 18 mcg/dL or 500 nmol/L). If your levels don’t rise adequately, it confirms adrenal insufficiency. Additional blood work measuring your ACTH level helps distinguish between primary and secondary causes: in primary insufficiency, ACTH will be elevated because the brain is trying harder to stimulate failing adrenals. In secondary insufficiency, ACTH will be low because the pituitary isn’t sending the signal.
“Adrenal Fatigue” Is Not the Same Thing
You may have encountered the term “adrenal fatigue” online, typically described as a state where chronic stress supposedly exhausts the adrenal glands and causes mild cortisol deficiency. The Endocrine Society, the leading professional organization for hormone specialists, states clearly that adrenal glands do not lose function from mental or physical stress. True adrenal insufficiency is a rare, diagnosable medical condition with specific lab findings. “Adrenal fatigue” has no accepted diagnostic criteria and no evidence supporting it as a distinct condition. The symptoms attributed to it, like tiredness and brain fog, are real but are better explained by other causes such as poor sleep, thyroid dysfunction, depression, or nutritional deficiencies.
Living With Low Cortisol
Adrenal insufficiency is a lifelong condition in most cases, but it’s manageable. Treatment replaces what the body can no longer make. The standard approach is oral hydrocortisone taken two or three times daily, with the largest dose in the morning to mimic the body’s natural rhythm and smaller doses in the afternoon. Total daily doses typically fall between 15 and 25 mg. People with primary adrenal insufficiency also need a second medication to replace aldosterone, a hormone the adrenal glands produce that regulates sodium and potassium balance. Unlike many hormonal conditions, doctors monitor cortisol replacement primarily through clinical assessment (your energy levels, weight, blood pressure, and whether you show signs of too much or too little replacement) rather than repeated blood tests.
The biggest adjustment is learning to manage “sick days” and physical stress. Your body normally surges cortisol production during illness, injury, or surgery. Since you can’t do that, you’ll need to increase your replacement dose during these periods, a practice called stress dosing. Annual visits with an endocrinologist include screening for related autoimmune conditions like thyroid disease, diabetes, and celiac disease, which are more common in people with autoimmune adrenal insufficiency. With consistent treatment and awareness of how to handle stress situations, most people with low cortisol maintain normal, active lives.