Low Cortisol Symptoms: What Could Be Causing Them and What to Do Next

Why Cortisol Matters More Than You Think

Cortisol is the body's primary glucocorticoid, produced by the adrenal cortex under direction from the hypothalamic-pituitary-adrenal (HPA) axis. It regulates blood pressure, blood glucose, immune response, and stress adaptation across a 24-hour circadian rhythm that peaks between 6 and 8 AM [1].

When cortisol production falls below physiologic need, symptoms emerge across multiple organ systems. The presentation can be subtle. Fatigue, lightheadedness on standing, unexplained weight loss, and nausea are common early complaints, but they overlap with dozens of other conditions, which is why low cortisol is frequently missed on initial evaluation [2]. A 2021 retrospective analysis published in the Journal of Clinical Endocrinology & Metabolism found that the median time from symptom onset to diagnosis of primary adrenal insufficiency was 1.1 years, with some patients waiting over 5 years [3].

The clinical consequences of missing the diagnosis are not trivial. Adrenal crisis, a life-threatening drop in cortisol during physiologic stress, carries a mortality rate of up to 6% per episode according to data from the European Adrenal Insufficiency Registry (EU-AIR, N=2,694) [4]. Understanding what drives cortisol deficiency is the first step toward preventing that outcome.

The Most Common Causes of Low Cortisol

Low cortisol falls into three mechanistic categories: primary adrenal insufficiency (the adrenal glands themselves fail), secondary adrenal insufficiency (the pituitary gland fails to produce adequate ACTH), and tertiary adrenal insufficiency (hypothalamic CRH suppression, almost always from exogenous glucocorticoids) [5].

Primary adrenal insufficiency (Addison disease). Autoimmune adrenalitis accounts for approximately 80% of cases in developed countries [2]. The immune system destroys the adrenal cortex, reducing production of cortisol, aldosterone, and adrenal androgens. Other primary causes include infections (tuberculosis remains the leading cause in endemic regions), bilateral adrenal hemorrhage, metastatic cancer infiltrating both glands, and rare genetic conditions like congenital adrenal hyperplasia and adrenoleukodystrophy [5].

Secondary and tertiary adrenal insufficiency. This is far more common than Addison disease. The single most frequent cause is iatrogenic: prolonged use of exogenous glucocorticoids (prednisone, dexamethasone, inhaled fluticasone at high doses, or even potent topical steroids) suppresses the HPA axis [6]. A systematic review in Annals of Internal Medicine found that any glucocorticoid course exceeding 4 weeks at supraphysiologic doses creates measurable HPA suppression risk [7]. Pituitary tumors, pituitary surgery, cranial radiation, traumatic brain injury, and Sheehan syndrome (postpartum pituitary necrosis) round out the secondary causes.

Drug-induced cortisol suppression beyond steroids. Checkpoint inhibitors (nivolumab, pembrolizumab) cause hypophysitis in 5% to 10% of treated patients, and opioid-induced adrenal insufficiency affects an estimated 9% to 29% of chronic opioid users based on a meta-analysis of 21 studies (N=2,279) published in Clinical Endocrinology [8]. The Endocrine Society's 2016 clinical practice guideline specifically recommends screening for adrenal insufficiency in patients on chronic opioids who present with fatigue and hypotension [5].

Recognizing the Symptom Pattern

The symptom profile of low cortisol varies depending on whether the deficiency is primary or secondary, how rapidly cortisol levels fell, and whether aldosterone production is also impaired.

Shared symptoms across all types include chronic fatigue that worsens with activity, orthostatic hypotension (systolic blood pressure drop of ≥20 mmHg on standing), nausea, decreased appetite, unintentional weight loss, and myalgias [2]. Hypoglycemia can occur, particularly in children or in adults who skip meals.

Primary-specific findings. Because the adrenal cortex is destroyed, ACTH rises without negative feedback. Elevated ACTH and its precursor (POMC) stimulate melanocyte receptors, producing hyperpigmentation of skin creases, buccal mucosa, and scars. Salt cravings develop from concurrent aldosterone deficiency, and hyperkalemia may appear on routine labs [5]. The Endocrine Society guideline notes: "Hyperpigmentation in a patient with fatigue and hyponatremia should prompt immediate evaluation for primary adrenal insufficiency" [5].

Secondary-specific findings. Skin pigmentation is normal or pale (ACTH is low, not high). Aldosterone is usually preserved because the renin-angiotensin system, not ACTH, is its primary regulator. Patients may have co-existing deficiencies in thyroid hormone, growth hormone, or gonadotropins depending on the extent of pituitary damage [9].

A common clinical trap: hyponatremia appears in both types but through different mechanisms. In primary disease it reflects volume depletion from aldosterone loss. In secondary disease it results from impaired free water excretion due to increased vasopressin (ADH) activity [2].

How Doctors Diagnose Low Cortisol

Diagnosis follows a logical sequence: screening, confirmation, and localization. The 2016 Endocrine Society Clinical Practice Guideline provides the standard algorithm [5].

Step 1: Morning serum cortisol. Blood drawn between 6 and 8 AM captures the circadian peak. A value <3 µg/dL (83 nmol/L) is virtually diagnostic of adrenal insufficiency, with sensitivity exceeding 95% in multiple validation cohorts [10]. A value above 15 µg/dL (414 nmol/L) effectively excludes the diagnosis. Values between 3 and 15 µg/dL require dynamic testing.

Step 2: Cosyntropin (ACTH) stimulation test. The standard test administers 250 µg of synthetic ACTH intravenously and measures cortisol at 0, 30, and 60 minutes. A peak cortisol <18 µg/dL (500 nmol/L) confirms adrenal insufficiency [5]. Dr. Stefan Bornstein, lead author of the Endocrine Society guideline and chair of medicine at Technische Universität Dresden, has stated: "The 250 µg cosyntropin test remains the most practical and well-validated first-line confirmatory test for adrenal insufficiency in clinical practice" [5].

Step 3: Differentiating primary from secondary. Simultaneously drawn plasma ACTH is the key discriminator. ACTH above 2 times the upper limit of normal with a low cortisol confirms primary disease. Low or inappropriately normal ACTH with low cortisol points to secondary or tertiary causes [5]. In primary disease, serum aldosterone will be low and plasma renin activity elevated. Adrenal antibodies (21-hydroxylase antibodies) are positive in roughly 85% of autoimmune cases [2].

Imaging. CT of the adrenals is indicated when primary disease is confirmed and the cause is unclear (looking for hemorrhage, infection, infiltration, or metastatic disease). MRI of the pituitary with gadolinium is performed when secondary disease is suspected [9].

Treatment: Replacing What the Body Cannot Make

The goal of treatment is to replicate the body's normal cortisol rhythm as closely as possible while preventing adrenal crisis during physiologic stress.

Glucocorticoid replacement. Hydrocortisone remains the first-line agent at a total daily dose of 15 to 25 mg, typically split into two or three doses: the largest in the morning (10 to 15 mg on waking) and a smaller dose in the early afternoon (5 to 10 mg) [5]. Some clinicians add a third 2.5 to 5 mg dose at midday for patients with persistent afternoon fatigue. Prednisolone (3 to 5 mg once daily) is an alternative for patients who prefer once-daily dosing, though its longer half-life may increase nocturnal cortisol exposure and impair sleep [11].

A modified-release hydrocortisone formulation (Plenadren) was approved by the EMA in 2011 and delivers a more physiologic cortisol profile with once-daily dosing. In a 12-week crossover trial (N=64), Plenadren reduced HbA1c by 0.2% and body weight by 0.9 kg compared with conventional thrice-daily hydrocortisone, suggesting less metabolic exposure [12].

Mineralocorticoid replacement. Patients with primary adrenal insufficiency need fludrocortisone, typically 50 to 200 µg daily, titrated to normalize blood pressure, potassium, and plasma renin activity [5]. Secondary adrenal insufficiency does not require fludrocortisone because aldosterone secretion remains intact.

Stress dosing and sick-day rules. Every patient with confirmed adrenal insufficiency needs education on stress dosing: doubling or tripling the oral hydrocortisone dose during febrile illness, and using intramuscular hydrocortisone 100 mg for vomiting, trauma, or inability to take oral medication [5]. The EU-AIR registry data showed that patients who had received structured crisis prevention education had 30% fewer emergency hospitalizations for adrenal crisis over 2 years compared with those who had not [4].

Medical alert identification. All patients should carry a steroid emergency card and wear medical alert identification. This is not optional guidance. It is a direct recommendation from the Endocrine Society guideline.

When Glucocorticoid Withdrawal Is the Cause

Among the causes of low cortisol symptoms, iatrogenic HPA axis suppression from exogenous steroids is the most common and also the most preventable. Any patient who has taken prednisone ≥5 mg daily (or equivalent) for more than 3 weeks is at risk for HPA suppression if the medication is stopped abruptly [6].

Recovery of the HPA axis follows a predictable but slow timeline. CRH secretion recovers first, followed by ACTH, and finally adrenal cortisol production. The median time to full recovery is 6 to 12 months, but some patients require 18 months or longer [7]. During this window, patients remain vulnerable to adrenal crisis if they encounter significant physiologic stress.

Standard taper protocols reduce the glucocorticoid dose by 10% to 20% every 1 to 2 weeks once the daily dose reaches physiologic range (equivalent to hydrocortisone 20 mg/day). Morning cortisol levels and ACTH stimulation tests guide decisions about when the taper can be completed and stress dosing can be discontinued [6].

Inhaled corticosteroids at high doses (fluticasone ≥1 to 000 µg/day or budesonide ≥800 µg/day) can also suppress the HPA axis, particularly in children. A systematic review identified 46 published cases of adrenal crisis linked to inhaled fluticasone, with 28 occurring in pediatric patients [13]. Clinicians should consider the lowest effective inhaled steroid dose and periodically reassess the need for high-dose therapy.

Less Common But Serious Causes to Rule Out

Several conditions can produce low cortisol that clinicians may overlook without a systematic differential.

Bilateral adrenal hemorrhage. This occurs most often in the setting of anticoagulation therapy, sepsis (particularly meningococcemia, known as Waterhouse-Friderichsen syndrome), or antiphospholipid syndrome. Onset is acute. CT shows bilateral adrenal enlargement with high-density areas. Without rapid glucocorticoid administration, mortality exceeds 50% [14].

Infiltrative disease. Metastatic carcinoma (lung, breast, melanoma), lymphoma, and granulomatous disease (sarcoidosis, histoplasmosis) can replace adrenal tissue bilaterally. Clinical adrenal insufficiency typically requires destruction of more than 90% of both glands [2].

Genetic causes. Congenital adrenal hyperplasia (CAH), most commonly 21-hydroxylase deficiency, is the leading genetic cause and affects approximately 1 in 15,000 live births [15]. X-linked adrenoleukodystrophy should be considered in males with primary adrenal insufficiency and neurologic symptoms. Autoimmune polyglandular syndrome types 1 and 2 can present with adrenal insufficiency alongside other autoimmune conditions such as type 1 diabetes, autoimmune thyroiditis, or hypoparathyroidism [2].

Checkpoint inhibitor hypophysitis. With the expanding use of immune checkpoint inhibitors in oncology, pituitary inflammation (hypophysitis) has become a well-recognized cause of secondary adrenal insufficiency. Anti-CTLA-4 agents (ipilimumab) carry a higher risk (up to 17% incidence) than anti-PD-1 agents (1% to 5%) [16]. ACTH deficiency from checkpoint inhibitor hypophysitis is often permanent, requiring lifelong glucocorticoid replacement even after the cancer treatment is completed.

Living With Low Cortisol: Practical Steps

Beyond medication, daily management of cortisol deficiency requires attention to several practical details that affect quality of life and safety.

Timing of hydrocortisone doses matters. Taking the first dose immediately upon waking (before getting out of bed, if possible) best mimics the natural cortisol surge and reduces morning symptoms of fatigue and orthostasis [11]. Patients should avoid taking hydrocortisone after 4 to 5 PM, as late dosing can disrupt sleep architecture.

Exercise tolerance often improves with a small supplemental dose (2.5 to 5 mg hydrocortisone) taken 30 to 60 minutes before planned vigorous activity. Sodium intake does not need to be restricted in primary adrenal insufficiency. In fact, patients on fludrocortisone should maintain liberal salt intake to support blood pressure [5].

Regular follow-up every 6 to 12 months should include clinical assessment of energy, weight, blood pressure (lying and standing), and electrolytes. Over-replacement, signaled by weight gain, insomnia, hyperglycemia, or reduced bone mineral density, is as important to detect as under-replacement [11]. Bone density screening (DXA) is recommended every 2 to 3 years in patients on long-term glucocorticoid replacement, as even physiologic doses may affect bone turnover over decades [5].

Adrenal crisis prevention remains the highest priority. Patients and their household contacts should know how to administer emergency intramuscular hydrocortisone (100 mg). A pre-filled syringe should be accessible at home, at work, and during travel.