Cycle-aware medicines: how menstruation shapes drug effectiveness
New evidence suggests women's menstrual cycles and fluctuating estrogen can alter how drugs are processed and how effective they are, with cycle phase influencing outcomes from vaccines to other medications. Estrogen modulates liver enzymes (CYPs) and brain blood flow, meaning the menstrual cycle should be treated as a variable rather than background noise in medical research. Early animal and small human data show higher drug uptake or different responses when estrogen is high, underscoring the need for cycle-aware pharmacology and more studies across medications.