Forgetting words mid-sentence. Walking into rooms and drawing a blank. Feeling like your brain is running on half power. If this sounds familiar, you're not alone — and you're not losing your mind. Perimenopause brain fog affects up to 44% of women in the hormonal transition, and it's driven by estrogen's direct role in brain energy. Here's the science behind it, why it's not dementia, and what actually helps.