Around 60 percent of women report brain fog during the menopause transition—a frustrating symptom marked by memory lapses, trouble focusing, and a general sense of mental fogginess. The most likely culprit? Estrogen decline. This hormone isn’t just about reproduction—it plays a critical role in brain function. Hormone replacement therapy (HRT, also called menopause hormone therapy or MHT) may improve brain health, including brain fog.