Hypocortisolism, a state of insufficient cortisol production, arises when the adrenal glands, the pituitary gland, or the hypothalamus fails at some point along the hormonal chain that normally keeps cortisol levels stable. The causes range from autoimmune destruction of the adrenals to infections, genetic enzyme defects, certain cancer drugs, and the surprisingly common problem of abruptly stopping prescribed steroids. Symptoms can be vague enough to be mistaken for depression or chronic fatigue for months or years, yet the condition can also escalate into a life-threatening emergency called adrenal crisis. Diagnosis hinges on blood tests and stimulation tests, but the details of those tests matter more than most patients realize.
Autoimmune and Infectious Causes
The single most common reason adults in developed countries develop primary adrenal insufficiency, historically called Addison’s disease, is an autoimmune attack on the adrenal cortex. The immune system produces antibodies against 21-hydroxylase, an enzyme the adrenal glands need to make cortisol and aldosterone. Autoimmunity accounts for roughly 75 to 96 percent of primary adrenal insufficiency cases in industrialized nations.1PubMed Central. The natural history of 21-hydroxylase autoantibodies in autoimmune Addison’s disease The destruction is gradual. By the time symptoms become obvious, about 90 percent of the adrenal cortex is typically gone.
Infections are a less common but still important trigger, particularly in regions where tuberculosis remains prevalent. Before autoimmune testing became widely available, TB was considered the leading cause of Addison’s disease worldwide. The adrenal glands can be infected by fungi, viruses, parasites, and bacteria, and the resulting tissue damage can impair hormone production either directly or through the inflammatory response it triggers.2International Journal of Infectious Diseases. Adrenal infections Fungal infections such as histoplasmosis and viral infections including cytomegalovirus are recognized culprits, particularly in people with weakened immune systems.3PubMed. Infectious causes of adrenal insufficiency
Genetic Causes
Congenital adrenal hyperplasia, or CAH, is a family of inherited conditions in which an enzyme needed to convert cholesterol into cortisol is missing or impaired. The most common form involves deficiency of the same 21-hydroxylase enzyme targeted in autoimmune Addison’s, but in CAH the deficiency is present from birth rather than acquired later. Because cortisol stays low, the pituitary gland keeps flooding the adrenals with stimulating hormone, causing them to enlarge while still failing to produce adequate cortisol.4Biology and management. Congenital adrenal hyperplasia: 21-hydroxylase deficiency and 11-hydroxylase deficiency
The severity ranges widely. In the most severe “salt-wasting” form, newborns can develop dangerous electrolyte imbalances within the first weeks of life. Sweden’s experience with newborn screening illustrates why early detection matters: before screening was introduced, two boys died during the neonatal period from adrenal crisis, and infants diagnosed clinically had dangerously low sodium levels. After screening began, the lowest sodium recorded at diagnosis was substantially higher, and only one severe salt-loss crisis occurred during the screening era.5PubMed. Benefits of neonatal screening for congenital adrenal hyperplasia (21-hydroxylase deficiency) in Sweden Milder “non-classic” forms of CAH may not surface until adolescence or adulthood and sometimes cause only subtle hormonal shifts.
Drug-Related and Iatrogenic Causes
The most underappreciated cause of hypocortisolism is also one of the most common: suppression of the body’s own cortisol production by prescribed glucocorticoids. When you take prednisone, dexamethasone, or similar drugs for more than a few weeks, your pituitary gland scales back its signals to the adrenals because exogenous steroids are already present. Stop the medication abruptly and the adrenals, having been idle, cannot ramp up production fast enough. The result is functional adrenal insufficiency that can persist for weeks or even months after the drug is discontinued. This is why doctors taper steroid doses gradually rather than stopping all at once.
A newer and increasingly relevant cause is immune checkpoint inhibitor therapy, used to treat various cancers. These drugs work by unleashing the immune system against tumors, but occasionally the immune system also targets endocrine glands. Checkpoint inhibitor-induced primary adrenal insufficiency is uncommon but potentially life-threatening. Patients typically present with fatigue, malaise, and nausea, and the condition may be mistaken for side effects of the cancer itself until cortisol levels are checked.6PubMed Central. Immune Checkpoint Inhibitor-Induced Primary Adrenal Insufficiency: A Case Report High-dose inhaled corticosteroids used for asthma can also suppress the adrenal axis over time, though this tends to produce milder insufficiency than oral steroids do.
Secondary and Tertiary Hypocortisolism
Not all cortisol deficiency starts at the adrenal glands. When the pituitary gland fails to secrete enough adrenocorticotropic hormone (ACTH), the adrenals receive no instruction to produce cortisol. This is called secondary adrenal insufficiency, and it can result from pituitary tumors, surgery on or near the pituitary, radiation to the head, or autoimmune inflammation of the pituitary (lymphocytic hypophysitis). Tertiary insufficiency, a step further up the chain, involves the hypothalamus failing to stimulate the pituitary. The iatrogenic steroid suppression described above is technically a form of tertiary insufficiency.
The practical difference between primary and secondary forms matters for symptoms and treatment. In primary disease the adrenals are damaged, so production of both cortisol and aldosterone typically drops. Aldosterone regulates salt and water balance, and its absence drives many of the electrolyte problems seen in Addison’s disease. In secondary and tertiary forms, aldosterone production usually remains intact because it is regulated primarily by the renin-angiotensin system rather than by ACTH alone. That distinction changes what replacement hormones a patient needs.
What Low Cortisol Feels Like
The hallmark symptoms of hypocortisolism are frustratingly nonspecific. Fatigue, weakness, loss of appetite, unintentional weight loss, low blood pressure, and dizziness on standing up are the most commonly reported complaints. Nausea, vague abdominal pain, and salt cravings round out the picture. Because these symptoms overlap with dozens of other conditions, the average time from first symptoms to diagnosis of Addison’s disease is often measured in months or years.
Cortisol plays a central role in maintaining blood sugar, particularly during periods of stress or fasting. When cortisol is insufficient, the body’s backup mechanisms for preventing blood sugar from dropping too low are compromised. This can lead to episodes of drowsiness, shakiness, and in severe cases seizures or collapse.7PubMed Central. Hypoglycaemia in adrenal insufficiency Newborns with cortisol deficiency are especially vulnerable to these episodes, but older children and adults remain at risk during illness or prolonged fasting.
Mood changes deserve mention because they are common yet frequently attributed to other causes. Depression, irritability, difficulty concentrating, and a general sense of mental “fogginess” are reported by many patients. These neuropsychiatric symptoms tend to improve with cortisol replacement, reinforcing the idea that cortisol has direct effects on brain function beyond just energy regulation.
Skin Changes and Electrolyte Shifts
One of the more distinctive signs of primary adrenal insufficiency is hyperpigmentation, a bronzing or darkening of the skin that often appears in skin creases, scars, the gums, and sun-exposed areas. The mechanism is tied to the feedback loop between the adrenals and the pituitary. When cortisol drops, the pituitary ramps up production of a precursor molecule from which both ACTH and a melanocyte-stimulating hormone are derived. The excess melanocyte-stimulating hormone drives increased pigment production in the skin.8BMJ Case Reports. Hyponatraemia and hyperpigmentation in primary adrenal insufficiency This sign is absent in secondary adrenal insufficiency, where ACTH levels are low rather than high, making it a useful clinical clue for distinguishing the two.
Electrolyte disturbances are common in primary disease because aldosterone deficiency allows sodium to be lost in the urine while potassium builds up in the blood. Low sodium (hyponatremia) is one of the most frequent lab findings and can cause confusion, headache, and in extreme cases seizures. High potassium (hyperkalemia) is the expected pattern, though rare exceptions occur. One case report documented a man with Addison’s disease who presented with dangerously low potassium of 2.3 mmol/L alongside a cortisol level of just 6 nmol/L, far below the normal range, and a massively elevated ACTH.9PubMed Central. Addison’s disease associated with hypokalemia: a case report Exceptions like this serve as a reminder that textbook presentations do not cover every patient.
Adrenal Crisis
Adrenal crisis is the most feared complication of hypocortisolism and is classified as an endocrine emergency with high mortality.10PubMed Central. Severe reversible cardiomyopathy associated with adrenal crisis caused by isolated adrenocorticotropin deficiency: a case report It typically occurs when someone with known or undiagnosed adrenal insufficiency faces a physiological stressor, such as an infection, surgery, or trauma, that demands a cortisol surge their body cannot deliver. Symptoms escalate rapidly: severe hypotension, shock, abdominal pain mimicking an acute abdomen, fever, and altered consciousness. Without prompt intravenous hydrocortisone and fluid resuscitation, adrenal crisis can be fatal.
Patients already diagnosed with adrenal insufficiency are taught “sick-day rules” for increasing their steroid dose during illness, and many carry injectable hydrocortisone for emergencies. The challenge is that a substantial number of crises happen before any diagnosis has been made. People with chronic fatigue and low-grade symptoms may coast along until a bout of gastroenteritis or a minor surgical procedure tips them into crisis.
How Diagnosis Begins
When hypocortisolism is suspected, the first step is usually a morning blood cortisol measurement, drawn between about 8 and 9 AM when cortisol naturally peaks. Guidelines from the Endocrine Society suggest that a morning cortisol below 3 µg/dL is strongly suggestive of adrenal insufficiency, while a level above 15 µg/dL generally rules it out.11PubMed Central. Morning cortisol and central adrenal insufficiency: new thresholds from low-dose ACTH test and second-generation assay Results between those thresholds fall into a gray zone and require further testing.
The standard follow-up is a stimulation test, most commonly the ACTH stimulation test. A synthetic form of ACTH is injected, and cortisol is measured at timed intervals to see whether the adrenals respond. A peak cortisol of 18 µg/dL or higher is traditionally considered a passing result. But the timing of that peak matters more than many clinicians realize. One study found that over half of patients reached their peak cortisol level at 60 minutes rather than at the conventional 30-minute mark, and about a quarter of patients who would have been classified as insufficient at 30 minutes actually passed when the test was extended to 60 minutes.12PubMed Central. THE LOW-DOSE ACTH STIMULATION TEST: IS 30 MINUTES LONG ENOUGH? Stopping the test too early risks mislabeling a patient as adrenally insufficient.
Another option gaining attention is salivary cortisol measurement, which captures the free (unbound) fraction of cortisol. Because saliva is not influenced by changes in the binding proteins that carry cortisol in the blood, salivary testing sidesteps certain lab artifacts that can confuse blood-based results.13PubMed Central. Salivary cortisol in the diagnosis of adrenal insufficiency: cost efficient and patient friendly It is also easier to collect repeatedly and does not require a needle, making it appealing for outpatient monitoring and for screening in children.
Telling Primary from Secondary Insufficiency
Once adrenal insufficiency is confirmed, the next diagnostic task is determining whether the problem is in the adrenals themselves (primary) or higher up in the pituitary or hypothalamus (secondary or tertiary). The simplest clue comes from ACTH levels: in primary insufficiency ACTH is high because the pituitary is working overtime trying to stimulate unresponsive adrenals, while in secondary insufficiency ACTH is low or inappropriately normal. An ACTH level above the upper limit of normal has been shown to distinguish primary from secondary disease with reasonable accuracy.14PubMed Central. Primary vs secondary adrenal insufficiency: ACTH-stimulated aldosterone diagnostic cut-off values by tandem mass spectrometry
A more refined approach uses stimulated aldosterone levels. Because aldosterone production depends on the adrenal gland’s zona glomerulosa, which is damaged in primary disease but relatively spared in secondary disease, measuring aldosterone after ACTH stimulation can add another layer of diagnostic clarity. A stimulated aldosterone below 5 ng/dL has shown roughly 88 percent sensitivity and about 90 percent specificity for identifying primary disease.14PubMed Central. Primary vs secondary adrenal insufficiency: ACTH-stimulated aldosterone diagnostic cut-off values by tandem mass spectrometry Imaging of the adrenals and the pituitary with CT or MRI rounds out the workup when the cause remains uncertain.
Lab Pitfalls That Lead to Misdiagnosis
A surprisingly common problem in cortisol testing is the assay itself. Most hospitals measure cortisol using immunoassays, which rely on antibodies to detect the hormone. These assays actually measure total cortisol, which includes cortisol bound to carrier proteins in the blood. In conditions that raise levels of corticosteroid-binding globulin, such as pregnancy or estrogen-containing oral contraceptives, the binding proteins compete with the assay’s own antibodies for cortisol molecules. The result can be falsely low readings, potentially leading to unnecessary diagnoses of adrenal insufficiency in people whose free cortisol is perfectly adequate.15PubMed Central. Are serum cortisol measurements by immunoassays reliable?: A case series
More accurate techniques such as liquid chromatography-tandem mass spectrometry exist but are not widely available in routine clinical settings. For patients whose test results do not match their clinical picture, particularly women on estrogen therapy, requesting a more specific assay or measuring salivary cortisol can help avoid a misdiagnosis. The ongoing shift toward newer cortisol assays is also changing the diagnostic thresholds that clinicians use. Cutoff values established with older assays may not apply to newer platforms, and clinicians sometimes apply old numbers to new assays without adjustment.
The Complexity of Replacement Therapy
Treatment for confirmed hypocortisolism centers on replacing the missing cortisol, typically with oral hydrocortisone taken two or three times a day. The challenge is that cortisol in a healthy body follows a pronounced daily rhythm, peaking in the early morning and dipping to its lowest point around midnight. Standard immediate-release hydrocortisone tablets cannot fully replicate that curve. Patients often experience a dip in cortisol between doses that leaves them feeling washed out, and there is no reliable blood marker clinicians can use to fine-tune the dose the way they can monitor, say, thyroid hormone replacement with a simple blood draw.16Karger. Long-acting hydrocortisone for glucocorticoid replacement therapy
Modified-release hydrocortisone formulations have been developed to better mimic the natural cortisol rhythm, releasing the drug gradually to produce a smoother blood-level profile. These are not available everywhere and tend to be more expensive, but they can improve quality of life for patients who struggle with the peaks and troughs of conventional dosing. Patients with primary disease also need fludrocortisone, a synthetic mineralocorticoid that replaces the missing aldosterone. In secondary insufficiency, fludrocortisone is usually unnecessary because aldosterone production is preserved, as noted earlier.
Dose adjustment during stress remains one of the trickiest aspects of living with adrenal insufficiency. The general rule is to double or triple the hydrocortisone dose during febrile illness, and to use injectable hydrocortisone for vomiting, surgery, or any situation where oral absorption might be compromised. Under-dosing during stress invites adrenal crisis; over-dosing on a chronic basis carries its own risks, including bone loss, weight gain, and metabolic disruption. Finding the right balance is an ongoing negotiation between patient and endocrinologist.
Over-the-Counter “Adrenal Support” Supplements
A booming supplement market caters to people who believe their cortisol levels are suboptimal, often under the unrecognized diagnosis of “adrenal fatigue.” While chronic stress can genuinely alter the way the hormonal stress axis functions,17The American Journal of Medicine. An Integrative Approach to HPA Axis Dysfunction: From Recognition to Recovery the products sold for this purpose raise serious safety concerns. A laboratory analysis of twelve over-the-counter “adrenal support” supplements found that all of them contained detectable thyroid hormone, and many contained steroid hormones including pregnenolone, budesonide (a potent glucocorticoid), androstenedione, and even cortisol itself.18PubMed. Over-the-Counter “Adrenal Support” Supplements Contain Thyroid and Steroid-Based Adrenal Hormones
The amounts detected were small on a per-tablet basis, but the presence of undeclared hormones in products marketed as dietary supplements means consumers are taking biologically active substances without knowing it. For someone who actually has adrenal insufficiency and is on prescribed replacement therapy, adding unregulated doses of cortisol or budesonide could interfere with their treatment. For someone without adrenal disease, chronic ingestion of exogenous glucocorticoids, even in small amounts, can suppress the body’s own cortisol production and create the very deficiency the supplement claims to fix. If you suspect your cortisol is low, the responsible path is a proper medical evaluation rather than self-treatment with unregulated products whose contents do not match their labels.