Bloodletting (or blood-letting) is the withdrawal of blood from a patient to prevent or cure illness and disease.
Bloodletting, whether by a physician or by leeches, was based on an ancient system of medicine in which blood and other bodily fluids were regarded as "humours" that had to remain in proper balance to maintain health. It is claimed to have been the most common medical practice performed by surgeons from antiquity until the late 19th century, a span of over 2,000 years.
In Europe, the practice continued to be relatively common until the end of the 18th century. The practice has now been abandoned by modern-style medicine for all except a few very specific medical conditions.
It is conceivable that historically, in the absence of other treatments for hypertension, bloodletting sometimes had a beneficial effect in temporarily reducing blood pressure by reducing blood volume. However, since hypertension is very often asymptomatic and thus not diagnosable without modern methods, this effect was unintentional. In the overwhelming majority of cases, the historical use of bloodletting was harmful to patients.
Bloodletting was used to treat almost every disease. One British medical text recommended bloodletting for acne, asthma, cancer, cholera, coma, convulsions, diabetes, epilepsy, gangrene, gout, herpes, indigestion, insanity, jaundice, leprosy, ophthalmia, plague, pneumonia, scurvy, smallpox, stroke, tetanus, tuberculosis, and for some one hundred other diseases.
Bloodletting was even used to treat most forms of hemorrhaging such as nosebleed, excessive menstruation, or hemorrhoidal bleeding. Before surgery or at the onset of childbirth, blood was removed to prevent inflammation. Before amputation, it was customary to remove a quantity of blood equal to the amount believed to circulate in the limb that was to be removed.
There were also theories that bloodletting would cure "heartsickness" and "heartbreak." A French physician, Jacques Ferrand wrote a book in 1623 on the uses of bloodletting to cure a broken heart. He recommended bloodletting to the point of literal heart failure.
Leeches became especially popular in the early nineteenth century. In the 1830s, the French imported about forty million leeches a year for medical purposes, and in the next decade, England imported six million leeches a year from France alone. Through the early decades of the century, hundreds of millions of leeches were used by physicians throughout Europe.