Blooletting (or blood-letting, in modern medicine referred to as phlebotomy) was a tremendously popular medical practice from antiquity up to the late 19th century, a time span of almost 2,000 years. Bloodletting involves the withdrawal of often considerable quantities of blood from a patient in the hopeful belief that this would cure or prevent a great many illnesses and diseases. The practice, of unproven efficacy, has been abandoned for all except a few very specific conditions. It is conceivable that historically, in the absence of other treatments for hypertension, bloodletting could sometimes have had an beneficial effect in temporarily reducing blood pressure by a reduction in blood volume. However since hypertension is almost always asymptomatic and thus undiagnosable without modern methods, this effect was unintentional. In the overwhelming majority of cases, however, the historical use of bloodletting has been downright harmful to the patient.