Brain Fog, Mood Swings, or Something Else? Naming Perimenopause Symptoms Patients Don't Expect
You lose the word for something you use every day. You snap at someone over nothing, then can't explain ten minutes later why it felt urgent. Somewhere between 44 and 62 percent of women report this during perimenopause, and a lot of them get told it's stress.
Last updated July 2026
You forget the word for something you use every day. You snap at your partner over nothing, then wonder ten minutes later why it felt so urgent. You lie awake at 2 a.m. running through a list of things that were fine yesterday. If you've searched "is this perimenopause or anxiety" at some point this year, you are not overreacting, and you are far from alone.
I'm Dr. Maria Clarinda Buencamino-Francisco, known to my patients as Dr. B. I'm a board-certified internal medicine physician and a Menopause Society Certified Practitioner (MSCP) at Concierge Medicine of the South Shore in Hingham, Massachusetts. This post covers the perimenopause symptoms that patients bring to me most often, the ones that rarely get connected to hormones on a first visit, and how to tell the difference between "this is stress" and "this is perimenopause."
Why These Symptoms Get Missed
Perimenopause is defined by fluctuating, not simply declining, estrogen and progesterone. That fluctuation is exactly why symptoms feel inconsistent and hard to pin down. A patient can feel completely fine for three weeks and then unravel for one, and that unpredictability is part of what makes the symptoms so easy to misattribute to stress, aging, or "just having an off week."
There's also a structural reason these symptoms get missed: a 15-minute primary care visit rarely leaves room to connect five seemingly unrelated complaints (memory lapses, mood, sleep, weight, joint aches) into one hormonal picture. Each symptom gets addressed in isolation, if it gets addressed at all.
Brain Fog: What It Actually Feels Like
Patients rarely use the term "cognitive impairment." They say things like losing their train of thought mid-sentence, walking into a room and forgetting why, or needing extra time to find a word that used to come instantly. According to a review from Utah State University Extension, an estimated 44 to 62 percent of women report this kind of subjective cognitive change during perimenopause, based on data from the Study of Women's Health Across the Nation and related cohort research.
A few things worth knowing about perimenopausal brain fog:
It tends to affect processing speed and word retrieval more than long-term memory.
Sleep disruption from night sweats can make it noticeably worse.
Research summarized in a 2026 Frontiers in Human Neuroscience review notes that these cognitive changes are usually modest, variable, and often improve after the menopause transition, rather than representing a progressive or degenerative condition.
I want to be direct about this one: brain fog in your 40s is not early dementia. It is a real, common, and typically temporary symptom of a hormonal transition, not a neurological diagnosis.
Mood Swings That Don't Match PMS
Patients often describe irritability or tearfulness that feels disproportionate to whatever triggered it, or mood shifts that no longer track with their menstrual cycle the way PMS once did. According to the American College of Obstetricians and Gynecologists, about 4 in 10 women experience mood symptoms during perimenopause that resemble PMS, but unlike PMS, these symptoms can appear at any point in the cycle and persist for years without a predictable pattern. ACOG also confirms that the overall risk of depression increases during the menopause transition itself.
This distinction matters clinically. A mood change tied to fluctuating estrogen and progesterone is addressed differently than a mood change with no hormonal component, and that difference should shape the treatment plan, not just the prescription pad.
Weight and Metabolism Shifts
Many patients notice their weight creeping up despite no real change in diet or activity, along with new fat distribution around the midsection. This is a metabolic shift, not a willpower failure, and it deserves its own clinical conversation rather than a generic "eat less, move more" response. I've written more specifically about this in Metabolic Health in Midlife: The Foundation of Lasting Energy and Wellbeing, which walks through why midlife metabolism behaves differently and what actually helps.
Joint Pain Nobody Connects to Hormones
Aching knees, stiff hands in the morning, or a new soreness in joints that never bothered you before: patients almost never bring this up as a "perimenopause question." They bring it up as a separate, unrelated complaint, often after already wondering if it's early arthritis. Estrogen has a role in joint and connective tissue health, which is one reason joint discomfort clusters with the same age range as other perimenopause symptoms, even though it rarely gets named as one.
Libido Changes Patients Rarely Bring Up First
This is often the symptom mentioned last, almost as an afterthought at the end of a visit. Reduced libido during perimenopause is common, has real physiological drivers, and does not need to be permanent or simply endured. It deserves the same direct, clinical conversation as any other symptom on this list, not silence.
A Patient Story
A patient in her mid-40s came to me convinced she was developing early Alzheimer's. She was losing words mid-sentence at work, snapping at her kids over small things, and waking at 3 a.m. most nights. She had already seen her prior PCP, who ordered basic bloodwork, found nothing alarming, and told her it was probably just stress. Nobody had asked about her cycle, her sleep pattern, or whether these symptoms clustered together. Once we mapped her symptoms against her actual hormonal timeline, the picture was clear: this was perimenopause, not neurological decline, and not "just stress." That reframe alone changed how she approached her own health, before we even discussed treatment options.
When to Ask Your Doctor About Perimenopause
If you're in your late 30s through 40s and recognize two or more of these symptoms happening together, here's what I recommend:
Track your symptoms against your cycle for two to three months, even if your cycle feels irregular.
Bring the full list to your appointment, not just the symptom that bothers you most. The pattern across symptoms is often more diagnostic than any single one.
Ask directly whether perimenopause has been considered, since it doesn't always come up unprompted in a short visit.
Ask about sleep specifically. Night sweats and fragmented sleep make brain fog and mood symptoms measurably worse, and they're often treatable on their own. My post on hot-night insomnia in perimenopause covers this in more depth.
If you've already been told your fatigue or mood is "just stress" more than once, it may be worth a second look. I wrote about this pattern in Fatigue, Stress, and Missed Diagnoses.
As I tell patients directly: these symptoms are not a character flaw or a sign you're falling apart. They're a hormonal pattern with a name, and naming it is the first step to addressing it.
In my practice, a visit long enough to actually map these symptoms against a patient's cycle and history is the difference between a diagnosis and another round of "let's watch and see." That's part of why I wrote about what a concierge model specifically changes for menopause care, separate from the symptoms themselves.
What to Watch for Next
Naming the symptom is only step one. The next question most patients ask is what actually helps, particularly around hormone therapy: what changed in the research, what's outdated advice from a decade ago, and what's still accurate today. That's the subject of an upcoming post on HRT in 2026, which will walk through the current evidence directly. [Internal link: forthcoming HRT pillar post, not yet published.]
If you're noticing a cluster of these symptoms and haven't had a straight answer yet, that conversation is exactly what a concierge visit at Concierge Medicine of the South Shore is built for. Call 781-795-9980 to ask about current availability.
