Perimenopause is the phase when ovarian hormone production becomes unpredictable, leading to symptoms such as cycle changes, sleep disruption, mood shifts, hot flashes, or brain fog. It can begin years before periods stop and often causes the most noticeable symptoms. Menopause is reached once someone has gone 12 consecutive months without a period and marks a stable, lower-estrogen state. Many people assume symptoms start after menopause, but they often begin during perimenopause.
