You wake up exhausted. Not just tired — genuinely depleted, as though sleep provided no restoration at all. Your brain feels slow. Your muscles feel heavy. Getting out of bed feels less like waking up and more like negotiating with a body that has flatly refused to cooperate.
What if this wasn't a willpower problem, or a sleep hygiene problem, or even a general "stress" problem — but rather the consequence of a single, measurable hormonal deficiency operating upstream of almost every symptom you experience?
That hormone is cortisol. And in people with ME/CFS and Long COVID, the system designed to produce it may be not just impaired, but structurally damaged — at the level of individual neurons in the brain.
What cortisol actually does — and why it matters so much
Cortisol is most commonly associated with "stress" — which has given it an unfairly negative reputation. In reality, cortisol is not the problem; it is the solution. It is one of the most critical regulatory hormones in the entire body, and understanding its full role makes clear just how devastating a deficiency can be.
Energy mobilisation
Raises blood sugar on waking and during exertion, enabling the body to actually utilise stored fat and protein for fuel. Without it, energy cannot be mobilised when needed.
Alertness & focus
The morning cortisol surge is what creates the feeling of being "awake." It sharpens attention, enables motivation, and helps the brain respond to challenges and decisions.
Anti-inflammatory action
Cortisol is the body's primary natural anti-inflammatory. It modulates immune responses and prevents chronic inflammatory cascades — which become unchecked when cortisol is low.
Cardiovascular regulation
Helps constrict blood vessels and maintain blood pressure. Low cortisol contributes to orthostatic intolerance and POTS-like symptoms — dizziness and racing heart on standing.
Memory, mood & motivation
Influences memory consolidation, mood regulation, and the sense of motivation. Deficiency contributes to the flat, disconnected feeling many patients describe.
Immune system calibration
Prevents both overactivation and underactivation of the immune system. Without cortisol, immune dysregulation becomes more likely — including autoimmune-like responses.
When you read that list through the lens of ME/CFS symptoms — profound fatigue, cognitive impairment, poor arousal, mood disruption, orthostatic intolerance, chronic inflammation — the overlap is not coincidental. Low cortisol may be the single mechanism that connects more ME/CFS symptoms together than any other.
The cortisol awakening response should peak sharply 20-30 minutes after waking. In ME/CFS, this morning surge is characteristically blunted or absent — removing the biological signal that tells the body to wake up, mobilise energy, and engage.
The HPA axis: when the stress-response system breaks down
To understand why cortisol is low in ME/CFS, you need to understand the system responsible for producing it — the Hypothalamic-Pituitary-Adrenal (HPA) axis. Under normal conditions, this is an elegant feedback loop. In ME/CFS, recent evidence suggests it may be structurally broken at the very top.
Interactive diagram
The HPA axis: how it should work vs. what happens in ME/CFS
"A recent brain autopsy study of severe ME/CFS patients revealed that the hypothalamus had almost no CRH-producing neurons left — a startling structural finding that fundamentally changes how we understand this disease."
— ME/CFS research literature, compiled from autopsy and HPA dysfunction studiesThis is not a subtle finding. The CRH-producing neurons of the hypothalamus are the command centre of the entire stress-response and energy-regulation system. Their near-total depletion in severe ME/CFS patients means the body has lost the ability to signal for cortisol production — regardless of how much the adrenal glands could theoretically produce.
The result is a system-wide cascade failure. No CRH signal means no pituitary activation, which means no adrenal stimulation, which means chronically low cortisol — and profound fatigue, poor arousal, unrefreshing sleep, impaired anti-inflammation, and autonomic dysfunction. Simultaneously.
The Long COVID connection: cortisol as a defining biomarker
If the HPA axis story was already significant for ME/CFS, a landmark study has dramatically amplified its importance for Long COVID — and in doing so, connected two of the most prevalent post-viral conditions of our time.
What this looks like in real life
Research findings become most meaningful when grounded in human experience. The following account, shared widely in Long COVID communities, illustrates how cortisol deficiency plays out — and what targeted treatment can sometimes achieve.
This account reflects a pattern seen in a subset of patients — though responses to treatment vary widely and this should not be taken as a recommendation. The critical insight is the pathway from symptom to biomarker test to targeted intervention. Standard care rarely reaches step two.
You might reasonably ask: if cortisol is low, why not simply prescribe more of it? Because the CRH-producing neurons themselves appear to be depleted or burned out, the core signal-generation system is compromised — not just the adrenal output. Simply adding artificial cortisol can sometimes have negative effects in ME/CFS patients when you bypass a feedback system without fixing its cause.
Individual responses vary widely. Some patients report significant benefit. Others see no improvement or worsening. This is precisely why any exploration of cortisol-based treatment must be conducted with a qualified endocrinologist or specialist in neuroendocrinology — not attempted independently.
Questions to take to your doctor
If you recognise these patterns in your own experience, the following questions can help open the right diagnostic conversations. The key is specifically requesting the right tests — because standard blood panels rarely catch HPA dysfunction.
Ask these specifically about cortisol & the HPA axis
- 01"Can we test my morning salivary cortisol — specifically the Cortisol Awakening Response (CAR)? And if indicated, a full 24-hour salivary cortisol profile?" (Serum cortisol is far less sensitive to subtle dysfunction.)
- 02"Is HPA-axis dysfunction or secondary adrenal insufficiency a possibility given my symptoms and history?" (This opens a different diagnostic pathway than primary adrenal failure.)
- 03"Given the Iwasaki Long COVID research, would it be appropriate to test cortisol as a biomarker given my post-viral history?" (Citing recent research by name can be effective with some clinicians.)
- 04"Could I be referred to an endocrinologist with experience in post-viral conditions or ME/CFS, given the complexity of HPA assessment?"
- 05"Are there non-pharmacological approaches to supporting cortisol rhythm — such as morning light exposure, sleep timing, or stress-response regulation — that we could begin while investigating further?"
What you can do now — without a prescription
Morning light exposure is one of the most powerful tools available. Natural light within the first 30 minutes of waking triggers a cortisol signal through the suprachiasmatic nucleus — literally prompting the brain's timing system to fire the cortisol awakening response.
Consistent waking time matters more than consistent bedtime for anchoring cortisol rhythm. The HPA axis is exquisitely sensitive to the timing of waking — irregular patterns disrupt the system's ability to mount an appropriate cortisol surge.
Nervous system regulation tools — breathwork, vagal stimulation, and pacing — reduce the burden on an already-depleted stress-response system. Protecting your energy envelope is, in part, protecting your cortisol system.
Anti-inflammatory nutrition supports the cortisol axis indirectly by reducing the inflammatory load that cortisol is normally responsible for managing.