If you’re in your late 30s, 40s, or early 50s and noticing changes in your mood, sleep, weight, periods, or energy… it’s not “just stress” or “getting older.”

It may be perimenopause - the transitional phase leading up to menopause - and it’s powered by hormonal shifts that start long before your period stops.

The tricky part?
These hormonal changes aren’t linear or predictable. They rise, fall, surge, and dip… often within the same month.

The good news is: once you understand what’s happening hormonally, everything starts making a lot more sense.

Let’s break down the three key hormones - oestrogen, progesterone, and testosterone - and how changes in each one can influence your mood, weight, sleep, and daily energy.

This is a practical, evidence-informed guide written to help you understand what’s normal, what’s common, and when to seek support.

What Exactly Is Perimenopause?

Perimenopause is the period of hormonal transition leading up to menopause (which is officially the 12-month anniversary of your last menstrual period).

For most women, it lasts 4–8 years, and typically begins in the 40s, but it can start earlier or later.

During this phase, your ovarian function declines gradually… and sometimes very un-gradually. That’s why symptoms can come and go, intensify, disappear, and feel unpredictable.

Common early perimenopause symptoms include:

• Sleep disturbances
• Increasing PMS
• Anxiety or irritability
• Shorter cycles
• Heavier bleeding
• Brain fog
• New sensitivities to stress
• Weight fluctuations
• Night sweats or hot flushes

The unifying cause behind many of these?

Hormone shifts.

Let’s look at each one.

Oestrogen: The Hormone of Vitality and Stability

Oestrogen is responsible for:

• Mood regulation
• Cognitive function
• Joint health
• Vaginal and bladder health
• Bone density
• Temperature regulation
• Menstrual cycle rhythm

What happens to oestrogen in perimenopause?

It doesn’t simply “decline.”
It becomes erratic.

In early perimenopause, oestrogen can swing from very high one cycle to very low the next. This is why symptoms can be inconsistent.

Symptoms linked to fluctuating oestrogen:

When oestrogen is high:

• Breast tenderness
• Irritability
• Heavier periods
• Water retention
• Mood swings

When oestrogen is low:

• Night sweats
• Hot flushes
• Brain fog
• Vaginal dryness
• Lower libido
• Increased anxiety

These ups and downs are one of the main reasons women in their 40s say they “don’t feel like themselves” anymore.

Progesterone: The Calming Hormone

Progesterone is naturally soothing. It supports:

• Sleep
• Mood stability
• Cycle regularity
• Anxiety reduction
• Temperature regulation

What happens to progesterone in perimenopause?

From the mid-40s onward, progesterone is usually the first hormone to decline, thanks to more frequent anovulatory cycles (months where you don’t ovulate).

Without ovulation, you don’t produce much progesterone - even if you still get a period.

Symptoms linked to low progesterone:

• Sleep difficulties (especially early waking)
• Heightened anxiety
• Irritability
• Shorter menstrual cycles
• PMS intensifying
• Feeling easily overwhelmed
• “Wired but tired” evenings

Many women describe this as feeling like their “stress threshold has shrunk.”
That’s the impact of losing progesterone’s naturally calming effect on the nervous system.

Testosterone: The Quiet Powerhouse

Although produced in smaller amounts than in men, testosterone plays a powerful role in women’s health.

It supports:

• Strength and muscle mass
• Libido
• Motivation
• Mood
• Cognitive sharpness
• Overall vitality

What happens to testosterone in perimenopause?

Testosterone declines more gradually over time, starting in the 30s, with small but meaningful drops across the 40s and 50s.

Symptoms linked to low testosterone:

• Reduced libido
• Lower motivation
• Slower muscle recovery
• Reduced vitality
• Feeling “flat” or less driven
•  Decreased strength

Some women also notice a change in body composition - gaining fat more easily and building muscle more slowly - partly tied to this hormonal shift.

How These Hormone Shifts Affect Daily Life

Hormones don’t work in isolation.
They interact constantly, influencing multiple systems in the body.

Here’s what women commonly experience:

1. Mood & Emotional Changes

Fluctuating oestrogen and falling progesterone can create:

• Anxiety
• Mood swings
• Irritability
• Sensitivity to stress 
• Crying more easily
• Increased PMS

Oestrogen influences serotonin and dopamine, while progesterone supports GABA - so when both are inconsistent, mood can feel unpredictable.

2. Sleep Disturbances

One of the earliest and most frustrating symptoms.

You may notice:

• Trouble falling asleep
• Waking at 2–4 am
•  Feeling “tired but wired” 
• Light, fragmented sleep

Low progesterone reduces your ability to switch off, and low oestrogen can trigger night sweats or temperature swings.

3. Weight & Body Composition Changes

Weight gain in perimenopause isn’t simply about “slowing metabolism.”

Hormone changes affect:

• Fat distribution (more abdominal storage)
• Hunger cues
• Muscle mass (declines with lower testosterone)
• Insulin sensitivity

This makes body changes normal - not a sign of failure or loss of discipline.

4. Energy Fluctuations

Women often describe:

• Afternoon crashes
• Feeling exhausted despite sleeping
• Difficulty sustaining focus
• Feeling “foggy” or slow processing

Because oestrogen supports energy production in the brain and mitochondria, fluctuating levels can leave energy feeling inconsistent.

So… What Can You Do?

While every woman’s experience is unique, evidence supports a few core strategies:

✔ Prioritise strength training

Supports testosterone, protects muscle, improves metabolism, and enhances mood.

✔ Build balanced meals with protein + fibre

Helps stabilise blood sugar and energy.

✔ Reduce stress load where possible

Your nervous system becomes more sensitive during this time - stress management isn’t optional.

✔ Support sleep with consistent routines

A cool bedroom, a predictable wind-down, and reducing late-day stimulants all help.

✔ Speak with your GP if symptoms are disruptive

Many women benefit from personalised support, including menopausal hormone therapy (MHT), if appropriate.

Final Thoughts

Perimenopause is a major hormonal transition - but it’s also a normal part of a woman’s life. Understanding what’s happening in your body doesn’t remove the challenges, but it gives you clarity, confidence, and language to seek the right support.

You’re not imagining it.
You’re not “losing it.”
You’re not alone.

Your body is shifting, and with the right tools, you can navigate this season with more ease, energy, and self-understanding.