Bloodletting*, practiced for over 5000 years, was used to manage various conditions by “rebalancing” the humors (phlegm, bile, and blood) as per Hippocratic medicine. Early medical practitioners, including barber-surgeons, used blades to remove blood, linking the practice to astrology to justify its timing. Prominent advocates like Guy Patin and Benjamin Rush mistakenly claimed its effectiveness, but deaths, including that of George Washington, highlighted its dangers. Despite widespread usage, the practice was abandoned by the late nineteenth century due to the lack of proven efficacy and its frequent harm to patients. Influential medical figures like Pierre-Charles-Alexandre Louis introduced data-driven analyses that debunked bloodletting’s effectiveness. Public and professional skepticism grew, culminating in the practice’s decline. Bloodletting, however, is still used in limited situations, such as treating polycythemia vera and hemochromatosis (a genetic disorder resulting in an excess of iron in tissues). Contemporary medicine, rooted in precise diagnostics, categorizes blood abnormalities scientifically, marking a shift from archaic treatments like bloodletting to evidence-based medicine.