And yet, even when accounting for changes in additional hormone players like progesterone and testosterone, women may still notice changes and still don't feel like themselves.

They often find themselves wondering:

Why am I so irritated by the little things? They never used to bother me before.

Where did my motivation go?

Why don't I have the energy to exercise?

Why does getting through the day feel like a full-body effort?

When did staying home with my dog start sounding better than spending time with the people I love?

It's easy to assume the loss of energy, spunk and patience is just part of aging or something that has to be endured.

But that's not likely the case.

There's an important, overlooked hormone at play here: cortisol

What is Cortisol?

Cortisol is a steroid hormone made in the adrenal glands — small glands that sit atop the kidneys. It is critical in:

• Regulating the stress response
• Maintaining blood sugar levels
• Supporting blood pressure
• Modulating inflammation and the immune response
• Influencing energy, mood and focus

And while cortisol often gets a bad reputation as the "stress hormone" we need to detox from, it's not the enemy. In fact, it's essential for life.

It is made by the body throughout the day and, in a healthy system, it follows a predictable daily rhythm — often referred to as the diurnal cortisol curve. Levels rise within the first 30 minutes after waking (referred to as the cortisol awakening response), then gradually decline throughout the day, reaching their lowest point at night.

This rhythm helps to regulate energy during the day and support restful sleep at night.

The HPA Axis — Your Internal Stress Command Center

Cortisol doesn't work on its own. It's part of a tightly regulated system known as the hypothalamic-pituitary-adrenal (HPA) axis.

Here's how it works:

• The brain perceives a stressor
• The hypothalamus releases corticotropin-releasing hormone (CRH) sending it to the pituitary gland
• The pituitary gland releases adrenocorticotropic hormone (ACTH) sending it to the adrenal glands
• The adrenal glands produce cortisol

This cascade prepares the body for action — commonly known as the "fight or flight" response — by:

• Increasing blood sugar for quick energy
• Raising blood pressure
• Sharpening focus and alertness
• Temporarily suppressing non-essential functions like digestion and reproduction

Once the stressor resolves, cortisol should return to baseline.

That's how the system is designed to work.

Not All Stress Is Conscious: The Role of "Hidden Stressors"

Here's where things get more interesting — and more relevant.

The HPA axis is activated by perceived stress, but that perception happens at the level of the brain — not always at the level of conscious awareness.

In other words, your body can be in a stress response even when you don't feel stressed.

These are what I often refer to as hidden stressors.

They include things like:

• Blood sugar fluctuations
• High viral load
• Poor or fragmented sleep
• Chronic inflammation or illness
• Overtraining or under-recovery
• Nutrient deficiencies
• Hormonal fluctuations (like those seen in perimenopause)

Even though you may not label these as "stress," the brain interprets them as threats to stability — and activates the HPA axis accordingly.

Why This Matters...

This helps explain a pattern that comes up often:

A woman says, "I'm not that stressed — I don't know why I feel this way."

And she means it.

From a psychological standpoint, she may not feel overwhelmed. But from a physiologic standpoint, her body may be experiencing repeated or sustained HPA axis activation throughout the day.

The result?

• Elevated or dysregulated cortisol patterns
• Increased fatigue despite adequate effort
• Mood changes without a clear emotional trigger
• A sense of being "off" that's hard to explain

Bringing It Back to Cortisol

When both visible stressors (life demands) and hidden stressors (internal physiologic signals) are present, the HPA axis can be activated far more often than we realize.

And if the system doesn't get enough time to reset, cortisol patterns begin to shift — not because the body is failing, but because it's adapting to what it perceives as a constant need for vigilance.

When the System Stops Resetting

In modern life, stress is rarely a one-time event.

Instead, it's chronic, cumulative, and often invisible:

• Work demands
• Caregiving for children or aging parents
• Relationship strain
• Sleep disruption
• Underlying inflammation or illness

For many women, these stressors intensify during perimenopause — a life stage already marked by biological change.

Repeated activation of the HPA axis without adequate recovery time can lead to HPA axis dysregulation.

This is often what people are referring to when they use the term "adrenal fatigue."

"Adrenal Fatigue": A Language Problem, Not a Physiology Problem

Let's clear something up.

The term "adrenal fatigue" isn't recognized as a formal medical diagnosis. And technically, it's not the adrenal glands themselves that are "fatigued."

But that doesn't mean the experience people are describing is incorrect.

What most women — and many clinicians — are actually referring to when they use the term adrenal fatigue is dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis.

In other words, this isn't a problem of the adrenal glands failing. It's a problem of how the brain and body are communicating and responding to stress.

And this concept is far from fringe.

A large body of research is indexed in the medical literature examining the HPA axis and how chronic stress impacts its function. This research shows that stress can alter:

• Baseline cortisol levels
• The natural rise-and-fall (diurnal rhythm) of cortisol throughout the day
• The body's responsiveness to new stressors

Importantly, these changes don't look the same in everyone.

Some individuals may have higher cortisol output. Others may show a flattened or blunted daily pattern. Both can be associated with experiences like fatigue, mood changes, sleep disruption, and reduced resilience to stress.

So while "adrenal fatigue" may not be the most precise term, it has persisted for a reason — it reflects a recognizable pattern of stress-related change that many women notice, especially during perimenopause.

Why Menopause Makes This More Complicated

Perimenopause doesn't just affect reproductive hormones — it also impacts the brain and stress-response systems.

Hormonal influence on the HPA axis

As hormone levels change (think declining progesterone and estrogen), neurotransmitters are affected.

While estrogen influences how we perceive stress, progesterone plays a critical role in how we regulate it.

Progesterone is broken down into compounds (most notably allopregnanolone) that enhance the activity of GABA (gamma-aminobutyric acid) — the brain's most inhibitory, or calming, neurotransmitter.

GABA acts as a natural brake on the nervous system and stress response. It helps:

• Quiet excessive brain activity
• Promote relaxation and sleep
• Inhibit overactivation of the stress response

GABA also modulates the HPA axis, helping to keep cortisol output in check.

What Happens When Progesterone Declines?

During perimenopause, progesterone levels often decline earlier and more steeply than estrogen due to reduced ovulation.

As progesterone drops:

• GABA activity decreases
• The nervous system becomes more excitable
• The "braking system" on the HPA axis weakens

This has direct consequences for cortisol regulation:

• The HPA axis is more easily activated
• Cortisol responses may be stronger or more prolonged
• The body has a harder time shifting out of "fight-or-flight"

In reality, this can feel like:

• Heightened anxiety or inner tension
• Feeling "wired but tired"
• Difficulty winding down at night
• Increased sensitivity to stressors that once felt manageable

Estrogen, Serotonin, and the Stress Response

Estrogen does far more than regulate reproductive tissues — it plays a central role in brain chemistry and stress regulation.

One of its key effects is on serotonin, a neurotransmitter involved in mood, emotional stability, and stress perception. Estrogen supports serotonin by:

• Increasing its production and availability
• Enhancing receptor sensitivity
• Slowing its breakdown

When estrogen levels fluctuate or decline — as they do in perimenopause — serotonin signaling becomes less stable.

This has two important downstream effects:

1. Mood becomes more vulnerable
Lower or more erratic serotonin activity is associated with increased anxiety, irritability, and low mood.

2. The stress response becomes more reactive
Serotonin helps regulate the brain's perception of stress and modulates activity within the HPA axis. When serotonin signaling is disrupted, the brain is more likely to interpret situations as stressful — and to activate the HPA axis in response.

The result?

• More frequent activation of the stress response
• Greater cortisol output in response to smaller triggers
• Slower return to baseline after stress

Putting It Together

When you combine:

• Reduced estrogen (affecting serotonin and stress perception)
• Reduced progesterone (affecting GABA and stress regulation)

You get a nervous system that is both:

• More reactive to stress
• Less efficient at recovering from it

From a physiologic standpoint, this reflects a shift in HPA axis regulation — where cortisol is not necessarily always "too high" or "too low," but less well controlled.

This helps explain why women in perimenopause often feel:

• More overwhelmed by stress
• More emotionally reactive
• More fatigued, even without obvious cause

It's not "just aging."
It's a shift in how the body processes and responds to stress.

Evaluating Cortisol

HPA axis dysregulation is often reflected in changes to the diurnal cortisol curve. In the research, this is commonly described as a blunting of the slope (less variation between morning and evening levels) and a reduction in the total cortisol output over the course of the day (sometimes referred to as the area under the curve).

With this in mind, when it comes to assessing cortisol, context matters.

Blood Testing

Blood cortisol testing is useful for identifying serious endocrine disorders like:

• Cushing's syndrome (excess cortisol)
• Addison's disease (insufficient cortisol)

However, it provides only a single snapshot in time. Levels can also be influenced by the stress of the blood draw itself, which may temporarily elevate cortisol.

Importantly, blood testing does not evaluate for HPA axis dysregulation. Rather, it helps determine whether the adrenal glands are producing cortisol within an expected range.

Salivary Cortisol

Salivary testing allows for multiple measurements throughout the day, offering insight into:

• The diurnal rhythm
• The cortisol awakening response
• Overall daily output

Because it captures cortisol at several points, salivary testing allows us to visualize the daily pattern of cortisol release.

And it's within this pattern — specifically the slope of the curve and the total output across the day — that signs of HPA axis dysregulation are most often identified.

Why This Gets Overlooked

Despite a substantial body of research on the HPA axis, it often gets sidelined in clinical care.

Why?

Because:

• It's complex
• It doesn't fit neatly into a single diagnosis
• There's no one-size-fits-all treatment
• It exists in the gray area between mental, hormonal, and lifestyle health

Modern medicine excels at identifying disease — but struggles with dysregulation.

Supporting Cortisol and the Stress Response

The goal is not to eliminate stress — that's not realistic or necessary.

The goal is to restore balance between activation and recovery — between your sympathetic ("go, go, go") state and your parasympathetic ("rest and restore") state.

Because when it comes to the HPA axis, it's not just about how much stress you have — it's about how often your body is being pulled into stress without enough time to come back down.

And that includes both visible stressors (work, relationships, life demands) and hidden stressors — the physiologic inputs your brain interprets as stress, even if you don't consciously feel overwhelmed.

Supporting cortisol, then, becomes less about "doing more" and more about reducing the total stress load your system is responding to.

Ways to support this include:

• Deep breathing exercises
• Taking a few minutes each day to rest — without being tied to productivity
• Eating consistent meals throughout the day
• Striving for adequate protein consumption and hydration
• Laughter and social connection
• Gentle movement

The Takeaway

Cortisol is not the villain of perimenopause and menopause — but it is a key player.

As estrogen and progesterone decline, the body's ability to regulate stress begins to shift. What changes isn't just hormone levels — it's how the brain and body perceive, respond to, and recover from stress.

At the same time, many women are navigating an increase in both visible stressors (career demands, family responsibilities, life transitions) and hidden stressors — the physiologic signals, like poor sleep, blood sugar fluctuations, or inflammation, that the brain quietly interprets as stress.

The result is a higher total stress load.

And when that load consistently exceeds the body's ability to recover, the HPA axis begins to adapt. Cortisol patterns shift — not because the body is broken, but because it's doing its best to keep up with ongoing demand.

This is why so many women in perimenopause describe feeling:

• More reactive to stress
• More easily overwhelmed
• More fatigued, even when they're "doing everything right"

Understanding this changes the conversation.

It moves us away from blaming a single hormone — or dismissing what women notice altogether — and toward a more complete picture of how the body is functioning.

Because the goal isn't to eliminate stress or chase perfect hormone levels.

It's to support the system as a whole — to reduce total stress load, improve recovery, and restore resilience.

And when that happens, women don't just "get through" this phase of life.

They start to feel like themselves again — maybe even better.