Bloodletting is the deliberate removal of blood from the body for therapeutic purposes, and despite its reputation as a relic of medieval medicine, it remains a standard, evidence-based treatment for several conditions today. The modern version usually goes by “therapeutic phlebotomy” and looks a lot like a routine blood draw, but the principle is the same one practiced for thousands of years: take blood out to make the patient better. What has changed is the reasoning. Ancient physicians bled patients to rebalance imaginary bodily fluids. Modern doctors do it to lower dangerously high iron levels, reduce thickened blood that threatens to clot, and even remove environmental pollutants that accumulate in the bloodstream.
A Brief History of Getting Bled
For most of recorded medical history, bloodletting was not a niche treatment but the default one. Ancient Egyptian, Greek, Indian, and Chinese medical traditions all practiced some form of it. The Greek physician Galen cemented the practice in Western medicine by tying it to the theory of four humors: blood, phlegm, yellow bile, and black bile. If you were sick, the thinking went, one of these fluids was out of balance, and draining some blood was the most direct fix. That framework dominated European medicine for well over a thousand years, and bloodletting was prescribed for everything from fevers to infections to mental illness.
The practice only began to lose its grip in the nineteenth century, when a French physician named Pierre Louis did something radical: he counted. In his 1836 publication on the effects of bloodletting in inflammatory diseases, Louis compared outcomes of pneumonia patients who were bled quickly after onset with those bled later. He found that rapid bloodletting was associated with higher mortality, leading him to conclude that there were “narrow limits to the utility” of the procedure. His approach was a pioneering step toward what we now call evidence-based medicine, and it planted the seeds for bloodletting’s eventual decline as a catch-all therapy.1PubMed. In defense of Pierre Louis who pioneered the epidemiological approach to good medicine
By the early twentieth century, bloodletting had largely fallen out of mainstream practice, dismissed alongside leeches and laudanum as symbols of pre-scientific medicine. But the story did not end there. As researchers developed better tools to measure what was actually happening inside the body, they discovered specific conditions where removing blood genuinely helps. The old practice found new, narrow, and well-justified homes.
Hereditary Hemochromatosis
The most common reason a doctor will prescribe therapeutic phlebotomy today is hereditary hemochromatosis, a genetic condition in which the body absorbs too much iron from food. Iron is essential in small amounts, but when it builds up over years, it deposits in the liver, heart, pancreas, and joints, eventually causing organ damage if left untreated. Phlebotomy is considered the only effective treatment for iron depletion in these patients.2Blood. Kinetics of Iron Depletion in Hereditary Hemochromatosis
The good news is that the condition is increasingly caught early through genetic testing and routine blood work, often before any organ damage has occurred. Treatment is straightforward: the patient has a unit of blood drawn every week or two until iron stores drop to a safe level, then switches to maintenance phlebotomies a few times a year. For many patients, those maintenance sessions can even be converted into regular blood donations, meaning the removed blood helps other people rather than going to waste.3PubMed Central. Diagnosis and management of hereditary hemochromatosis: lifestyle modification, phlebotomy, and blood donation When diagnosed and treated early, the prognosis is excellent.
Polycythemia Vera
Polycythemia vera is a blood cancer in which the bone marrow produces too many red blood cells, thickening the blood and dramatically raising the risk of clots, strokes, and heart attacks. Phlebotomy is the frontline treatment because it directly reduces the volume of red blood cells, thinning the blood back toward normal.
The evidence here is strong. A landmark trial published in the New England Journal of Medicine followed over 350 patients and found that those whose hematocrit (a measure of red blood cell concentration) was kept below 45% through aggressive phlebotomy had a cardiovascular death and major clotting rate of about 3%, compared with roughly 10% in patients managed to a higher target. The difference in risk was nearly fourfold.4PubMed. Cardiovascular events and intensity of treatment in polycythemia vera That trial essentially settled the question: keeping the hematocrit below 45% with regular phlebotomy saves lives. For many patients with polycythemia vera, therapeutic bloodletting is not optional. It is the thing that keeps them from having a stroke.
Porphyria Cutanea Tarda
A third condition treated with phlebotomy is porphyria cutanea tarda, a disorder where the body cannot properly make heme, the iron-containing part of hemoglobin. The result is a buildup of porphyrins, chemicals that make the skin painfully sensitive to sunlight. Blisters, scarring, and fragile skin on sun-exposed areas are the hallmarks.
Iron plays a key role in driving the enzyme dysfunction behind this condition, so reducing iron stores through phlebotomy works well. In studies of patients bled until their iron stores dropped to mildly deficient levels, abnormal porphyrin excretion fell to normal or near-normal in an average of about four months. The improvement continued even after phlebotomy was stopped, suggesting that the effect is durable rather than requiring continuous treatment.5PubMed. Phlebotomy treatment of porphyria cutanea tarda For patients who cannot tolerate the alternative drug treatment (low-dose chloroquine), phlebotomy is the primary option.
Medicinal Leeches in Modern Surgery
If therapeutic phlebotomy is bloodletting dressed in modern scrubs, medicinal leeches are bloodletting in its most ancient costume still walking the hospital corridors. The use of leeches in reconstructive and microsurgery is one of the more surprising facts of modern medicine, but it is standard practice in many major hospitals.
The problem leeches solve is venous congestion. After surgeries that involve reattaching severed fingers, transplanting tissue flaps, or reconstructing ears and other delicate structures, blood sometimes flows into the reattached tissue through arteries but cannot drain back out through veins. The tissue swells, turns blue, and risks dying from the resulting pressure and oxygen deprivation. Leeches address this by feeding on the congested blood, and more importantly, by injecting saliva packed with over 100 bioactive compounds. These include hirudin, a potent anticoagulant, along with anti-inflammatory molecules, pain-reducing substances, and agents that promote the growth of new blood vessels.6PubMed Central. Molecular Insights into Leech-Derived Bioactive Compounds: Biochemical Mechanisms and Therapeutic Potential The anticoagulant effect is especially useful because the bite site continues to ooze blood for hours after the leech detaches, providing ongoing drainage for the congested tissue.
Leech therapy is considered a complement to surgery rather than a replacement for it. A review of the literature found that leeches can protect tissue flaps against venous obstruction, delayed blood flow, clotting, and the damage that comes when blood supply is interrupted and then restored.7PubMed Central. Leech Therapy Protects Free Flaps against Venous Congestion, Thrombus Formation, and Ischemia/Reperfusion Injury: Benefits, Complications, and Contradictions The technique is not exotic or fringe; it is a recognized tool in the plastic surgeon’s kit, and the FDA has cleared medicinal leeches as a medical device.
The Infection Risk with Leeches
Leeches come with a specific and well-documented complication: infection from Aeromonas bacteria. These bacteria live naturally in the leech’s digestive tract, where they help the animal break down ingested blood.8PubMed Central. Infections following the application of leeches: two case reports and review of the literature When leeches are applied to a surgical site, these bacteria can be introduced into the wound, and infections following leech therapy are the most commonly reported complication. For that reason, prophylactic antibiotics are recommended before and during leech treatment.9PubMed Central. Preventing Infective Complications following Leech Therapy: Elimination of Symbiotic Aeromonas spp. from the Intestine of Hirudo verbana Using Antibiotic Feeding
Even with prophylaxis, resistant infections can occur. At least one reported case involved an Aeromonas strain resistant to the ceftriaxone antibiotic given as a preventive measure, meaning the infection developed despite the patient being on the “right” drug.10PubMed. Ceftriaxone-Resistant Aeromonas hydrophila Infection Following Leech Therapy: A New Resistant Strain Surgeons weigh this risk against the potential loss of the tissue or limb they are trying to save, and in most cases, the balance tips in favor of the leeches. But it is a genuine risk that requires monitoring.
Wet Cupping and Hijama
Outside of hospital settings, bloodletting persists in traditional medicine systems around the world. The most widespread form is wet cupping, known in Arabic and Islamic medical traditions as hijama. The procedure involves placing suction cups on the skin to draw blood to the surface, then making small incisions and reapplying the cups to extract a small quantity of blood. It has been practiced continuously for centuries across the Middle East, North Africa, and parts of Asia, and has grown in popularity in Western countries, particularly among athletes and people seeking alternatives to pharmaceutical pain management.
The proposed mechanisms behind wet cupping are varied and not fully established. Several theories have been offered, including the idea that the controlled injury triggers pain-gate responses (where one sensation overrides another), stimulates nitric oxide release to improve local blood flow, and activates immune system responses.11PubMed Central. The medical perspective of cupping therapy: Effects and mechanisms of action Animal research has added some specificity. In rats, wet cupping was associated with significantly higher levels of beta-endorphin (the body’s own painkiller) and heat shock protein 70 in treated skin compared to controls, and pain thresholds after treatment roughly doubled.12Iranian Journal of Medical Sciences. Pain Relief with Wet Cupping Therapy in Rats is Mediated by Heat Shock Protein 70 and ß-Endorphin
The honest assessment is that the evidence base for wet cupping is far thinner than for therapeutic phlebotomy. Many studies are small, lack proper controls, or are conducted in populations already favorable to the practice. Wet cupping should not be confused with the clearly established medical uses of phlebotomy for hemochromatosis or polycythemia vera. It occupies a different tier of evidence entirely, and anyone considering it should understand that distinction.
The Iron Hypothesis and Heart Disease
One of the more intriguing threads in modern bloodletting research is the “iron hypothesis,” which suggests that lower iron stores protect against heart disease. The idea was originally proposed to explain why premenopausal women, who lose iron through menstruation, have lower rates of heart attack than men of the same age. If regular iron loss is protective, then blood donation, which also lowers iron stores, might offer similar benefits.
The evidence here is genuinely mixed, and the disagreement matters. A Finnish cohort study (the Kuopio Ischaemic Heart Disease Risk Factor Study) followed nearly 2,900 middle-aged men for about nine years and found that recent blood donors had a dramatically lower rate of heart attack, with an adjusted risk reduction of about 88% compared to non-donors.13American Journal of Epidemiology. Donation of Blood Is Associated with Reduced Risk of Myocardial Infarction: The Kuopio Ischaemic Heart Disease Risk Factor Study Another study found that blood donation in non-smoking men was associated with a roughly 33% lower odds of cardiovascular events.14PubMed Central. Possible association of a reduction in cardiovascular events with blood donation
But a large study published in Circulation found no such benefit. Despite the fact that frequent blood donors had substantially lower ferritin (a marker of iron stores), there was no reduction in heart attack or fatal coronary heart disease risk. Men who had donated 30 or more times in their lives had roughly the same risk as men who never donated.15PubMed. Blood donations and risk of coronary heart disease in men The iron hypothesis remains alive in research circles but unproven. Nobody should be giving blood primarily to prevent heart attacks based on current evidence.
Iron, Insulin, and Blood Vessel Function
A related line of research has looked at whether lowering iron through blood donation improves metabolic health, specifically insulin sensitivity and blood vessel function. One study found that frequent blood donors had significantly better insulin sensitivity and lower insulin secretion than non-donors, along with lower ferritin levels.16PubMed. Iron stores, blood donation, and insulin sensitivity and secretion That finding was suggestive, but a later study designed to test the same idea more carefully came to a more modest conclusion: high-frequency blood donors had lower ferritin and slightly better blood vessel dilation, but no actual improvement in insulin sensitivity or protection against the vascular effects of a sugar spike.17PubMed. Insulin sensitivity, vascular function, and iron stores in voluntary blood donors
The pattern across this research is that lowering iron stores through blood removal consistently reduces ferritin levels (unsurprisingly) and sometimes improves individual markers, but the downstream health benefits remain uncertain. The body of evidence is not strong enough to recommend therapeutic phlebotomy or frequent blood donation as a metabolic health intervention outside of the established conditions like hemochromatosis.
Removing Environmental Pollutants from Blood
A surprising modern application of bloodletting has nothing to do with iron. Australian firefighters exposed to PFAS (per- and polyfluoroalkyl substances, the so-called “forever chemicals” found in firefighting foam) participated in a randomized trial testing whether blood and plasma donations could reduce their body burden of these persistent pollutants. The results were striking: over 12 months, plasma donation significantly reduced levels of PFOS by about 2.9 ng/mL, and blood donation reduced PFOS by about 1.1 ng/mL, while levels in the observation group stayed the same. Plasma donation was more effective than blood donation overall, and both were clearly better than doing nothing.18PubMed Central. Effect of Plasma and Blood Donations on Levels of Perfluoroalkyl and Polyfluoroalkyl Substances in Firefighters in Australia: A Randomized Clinical Trial
PFAS contamination is a growing public health concern because these chemicals persist in the body for years and have been linked to various health problems. The fact that a form of bloodletting can measurably reduce them opens up a potential intervention for heavily exposed populations. This is still early research, and there are ethical questions about whether blood removed from PFAS-exposed individuals should enter the general blood supply, but it represents a genuinely novel use of an ancient technique.
Plasma Exchange and Alzheimer’s Disease
Therapeutic plasma exchange, or plasmapheresis, is a more aggressive modern cousin of bloodletting. Instead of simply removing whole blood, the procedure filters out the liquid portion (plasma) and returns the blood cells to the patient, replacing the plasma with albumin or donated plasma. It is already an established treatment for certain autoimmune conditions, but researchers have begun investigating whether it might slow the progression of Alzheimer’s disease by removing toxic factors that accumulate in the blood.
The idea draws partly from parabiosis research in mice, where exposure to young blood improved cognitive function in older animals. In humans, a 14-month trial of 322 Alzheimer’s patients found that plasma exchange with albumin-enriched replacement slowed cognitive, functional, and clinical decline, especially in patients with moderate disease.19PubMed Central. Perspective: Is therapeutic plasma exchange a viable option for treating Alzheimer’s disease? A more recent real-world study reported that patients receiving plasma exchange showed about 45% less decline on a standard cognitive test compared to controls, with even larger differences in memory-specific measures.20PubMed Central. A real-world study on the safety and efficacy of therapeutic plasma exchange in patients with Alzheimer’s disease
These results are preliminary and should not be taken as proof that plasma exchange treats Alzheimer’s. The research is at an early stage, and the procedure is invasive, expensive, and not without risk. But the idea that periodically cleaning the blood might slow neurodegeneration is a fascinating extension of the bloodletting principle into entirely new territory.
How Safe Is Modern Therapeutic Phlebotomy?
For straightforward phlebotomy (the kind used for hemochromatosis and polycythemia vera), the safety profile is reassuring. A prospective study tracking 587 therapeutic phlebotomy procedures found that adverse events occurred in about 4% of sessions, nearly all of them vasovagal reactions (the lightheaded, clammy feeling you can get from any blood draw). None of the reactions were clinically serious, and all were managed on-site by nursing staff with full patient recovery.21PubMed. Adverse effects of therapeutic phlebotomies: Prospective study of 587 procedures For most patients, the experience is essentially identical to donating blood.
Risks increase with more invasive forms of bloodletting. Leech therapy carries the Aeromonas infection risk discussed earlier. Plasma exchange involves more complex equipment and can cause reactions to the replacement fluids, drops in blood pressure, and electrolyte imbalances. Wet cupping performed by untrained practitioners carries risks of scarring, infection, and excessive blood loss. As with any medical procedure, the risk-benefit calculation depends entirely on what condition is being treated and who is doing the treating.
Leeches at the Veterinary Clinic
Medicinal leeches are not reserved for humans. Veterinary surgeons have adopted leech therapy for the same indication it serves in human medicine: salvaging tissue with compromised venous drainage after reconstructive procedures. A retrospective study of animals treated with medicinal leeches found that three-quarters of patients showed clear improvement in the affected tissue following treatment.22PubMed. Medicinal Leech Therapy in Veterinary Medicine: A Retrospective Study Dogs, cats, and horses can all develop the same venous congestion problems that afflict human microsurgery patients, and leeches offer the same solution. The concept translates directly across species because the underlying vascular problem is the same.
Veterinary leech therapy faces many of the same challenges as the human version: the need for antibiotic prophylaxis against Aeromonas, the requirement for trained personnel to manage the leeches, and the fact that the animals are not always enthusiastic participants. Still, for a surgeon watching a tissue flap turn dusky blue and knowing that the alternative is losing it entirely, a few leeches can be the difference between a successful outcome and a failed reconstruction.