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.

[12] According to some accounts, the Egyptians based the idea on their observations of the hippopotamus,[13] confusing its red secretions with blood and believing that it scratched itself to relieve distress.

[14][15] In Greece, bloodletting was in use in the 5th century BC during the lifetime of Hippocrates, who mentions this practice but generally relied on dietary techniques.

During the Roman Empire, the Greek physician Galen, who subscribed to the teachings of Hippocrates, advocated physician-initiated bloodletting.

[18] The popularity of bloodletting in the classical Mediterranean world was reinforced by the ideas of Galen, after he discovered that not only veins but also arteries were filled with blood, not air as was commonly believed at the time.

Galen created a complex system of how much blood should be removed based on the patient's age, constitution, the season, the weather and the place.

The blood to be let was of a specific nature determined by the disease: either arterial or venous, and distant or close to the area of the body affected.

[23] According to Helena Miton et al.'s [22] analysis of the HRAF database and other sources, there are several cross-cultural patterns in bloodletting.

The practice was probably passed by the Greeks with the translation of ancient texts to Arabic and is different than bloodletting by cupping mentioned in the traditions of Muhammad.

Together with cautery, it was central to Arabic surgery; the key texts Kitab al-Qanun and especially Al-Tasrif li-man 'ajaza 'an al-ta'lif both recommended it.

Bloodletting became a main technique of heroic medicine, a traumatic and destructive collection of medical practices that emerged in the 18th century.

Bloodletting was used to "treat" a wide range of diseases, becoming a standard treatment for almost every ailment, and was practiced prophylactically as well as therapeutically.

The withdrawal of so much blood as to induce syncope (fainting) was considered beneficial, and many sessions would only end when the patient began to swoon.

William Harvey disproved the basis of the practice in 1628,[2] and the introduction of scientific medicine, la méthode numérique, allowed Pierre Charles Alexandre Louis to demonstrate that phlebotomy was entirely ineffective in the treatment of pneumonia and various fevers in the 1830s.

Nevertheless, in 1838, a lecturer at the Royal College of Physicians would still state that "blood-letting is a remedy which, when judiciously employed, it is hardly possible to estimate too highly",[28] and Louis was dogged by the sanguinary Broussais, who could recommend leeches fifty at a time.

Some physicians resisted Louis' work because they "were not prepared to discard therapies 'validated by both tradition and their own experience on account of somebody else's numbers'.

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.

A French sergeant was stabbed through the chest while engaged in single combat; within minutes, he fainted from loss of blood.

Within a ten-hour period, a total of 124–126 ounces (3.75 liters) of blood was withdrawn prior to his death from a throat infection in 1799.

[34] One reason for the continued popularity of bloodletting (and purging) was that, while anatomical knowledge, surgical and diagnostic skills increased tremendously in Europe from the 17th century, the key to curing disease remained elusive, and the underlying belief was that it was better to give any treatment than nothing at all.

[36] Barbara Ehrenreich and Deirdre English write that the popularity of bloodletting and heroic medicine in general was because of a need to justify medical billing.

In the medical community of Edinburgh, bloodletting was abandoned in practice before it was challenged in theory, a contradiction highlighted by physician-physiologist John Hughes Bennett.

[38] Some physicians considered bloodletting useful for a more limited range of purposes, such as to "clear out" infected or weakened blood or its ability to "cause hæmorrhages to cease"—as evidenced in a call for a "fair trial for blood-letting as a remedy" in 1871.

[45] Though bloodletting as a general health measure has been shown to be pseudoscience, it is still commonly indicated for a wide variety of conditions in the Ayurvedic, Unani, and traditional Chinese systems of alternative medicine.