Perimenopause
The years before your last period — usually starting in the mid-to-late 40s, lasting 4–10 years. During this time, every hormone axis in the body destabilises simultaneously. It is not just a “hormonal thing.” It affects bone, heart, brain, metabolism, bladder, joints, sleep, and mood.
What is actually happening
The ovarian follicle pool is depleting. From birth, a woman has a finite number of follicles. From the mid-30s, the pool shrinks faster. By the mid-40s, it is small enough that estrogen and progesterone production becomes erratic rather than cyclical.
It is not a smooth decline — it is chaos first, then decline. Estrogen can spike higher than normal in early perimenopause (causing breast tenderness, heavy periods, anxiety) and crash the next month. This erratic volatility, not just low levels, is why symptoms feel so disorienting.
Progesterone falls first. As ovulation becomes irregular, progesterone production in the luteal phase disappears. This is why anxiety, sleep disruption, and mood changes often arrive before the classic vasomotor symptoms.
Three axes destabilise simultaneously. The HPO (reproductive), HPA (stress), and metabolic axes all interact and all shift. Declining estrogen dysregulates cortisol. Cortisol disrupts sleep. Poor sleep suppresses growth hormone. Insulin resistance rises. Each worsens the others.
- ✗“You're too young” — onset in the mid-40s is normal. Late 30s is not rare.
- ✗“Your bloods are normal” — hormones fluctuate wildly. One normal test on the wrong day tells you nothing.
- ✗“It's just anxiety/stress” — mood and cognitive symptoms have specific hormonal drivers.
- ✗“Everyone goes through this” — common yes. Something to simply endure, no.
Bone loss, cardiovascular changes, and metabolic shifts all begin in perimenopause — years before menopause. Intervention during the “window of opportunity” (before 60, or within 10 years of menopause) is most effective. Women dismissed for years miss this window.
Everything in the perimenopause guide
All 10 symptom clusters — what each one is, why it happens biologically, and what tests to ask for. From hot flashes to brain fog to joint pain.
When different symptoms typically appear across the transition — from early perimenopause through menopause and into post-menopause.
Evidence-rated treatments for each symptom cluster — hormonal (HRT), non-hormonal, supplements, and lifestyle. Each rated by trial quality.
What to ask your doctor to test, when to test it, what normal means (and why normal is often misleading in perimenopause), and how to interpret results.
14 hormones explained — estrogen, progesterone, testosterone, cortisol, insulin, thyroid and more. What each does and what happens when it shifts.
How the HPO axis, HPA stress axis, and metabolic web all connect — and how perimenopause disrupts all three simultaneously.
All citations — SWAN, NAMS, WHI, Endocrine Society guidelines, and primary research papers. Every claim is sourced.