Medicinal leech therapy, also called hirudotherapy, is the controlled clinical use of blood-feeding leeches to relieve venous congestion and, in some settings, to provide other therapeutic effects. Modern medicine uses specially supplied medicinal leeches most often when blood can enter transplanted, replanted, or reconstructed tissue through arteries but cannot drain adequately through veins.

The leech provides two related effects. First, it removes congested blood while feeding. Second, substances introduced in its saliva interfere with clotting and platelet activity, allowing the bite site to continue bleeding after the leech detaches. This prolonged local blood loss can temporarily substitute for inadequate venous drainage while new venous connections develop or other treatment becomes possible.

Medicinal leeches are living therapeutic organisms and therefore present unusual issues involving infection control, blood loss, product quality, antibiotic prophylaxis, and animal handling. In the United States, medicinal leeches are FDA-regulated medical devices cleared for use in managing venous congestion.

These 20 questions explain what leech therapy is, how it works, when it is used, what the major risks are, how medicinal leeches are regulated and managed, and what the scientific evidence shows.

At a Glance: Modern Medicinal Leech Therapy

Question Key point
Main established medical use Temporary relief of venous congestion, especially in grafts, flaps, and replanted tissue
How does it work? The leech removes blood and introduces salivary substances that prolong local bleeding
Main species used FDA-cleared products include medicinal leeches identified as Hirudo medicinalis and Hirudo verbana
Major risks Blood loss/anemia and infection, especially from Aeromonas species
Are antibiotics commonly used? Yes, prophylaxis active against leech-associated bacteria is commonly recommended in reconstructive use
Can a leech be reused? No. It is treated as a single-use biological medical device
Can transfusion be required? Yes, especially during prolonged or repeated therapy
FDA status 510(k)-cleared medicinal leech products are available for venous-congestion indications
FDA oversight Regulatory responsibility transferred from CDRH to CBER in December 2024 because medicinal leeches are living therapeutic organisms

QUESTIONS

  1. What is leech therapy (hirudotherapy)?

Medicinal leech therapy is the deliberate application of specially supplied blood-feeding leeches to a patient for a therapeutic purpose.

In modern hospital practice, its most important role is treating venous congestion (a condition in which arterial blood reaches a piece of tissue but venous blood cannot drain away adequately).

This can occur after:

  • replantation of a severed finger, ear, lip, or other body part;
  • reconstructive flap surgery;
  • skin or tissue grafting;
  • microsurgery in which small veins cannot be repaired successfully; or
  • other procedures in which venous outflow is temporarily inadequate.

The leech removes congested blood directly while feeding. After detachment, the wound may continue to bleed for hours because salivary substances interfere with clotting and platelet function.

FDA describes medicinal leeches as an adjunct to graft-tissue healing when venous congestion may delay healing, or as a way of overcoming venous congestion by producing prolonged localized bleeding.

  1. What conditions is leech therapy used for?

The best-established modern indication is venous congestion in reconstructive and microsurgical tissue.

Examples include:

  • congested skin flaps;
  • replanted fingers;
  • reattached ears;
  • nasal or facial tissue;
  • breast-reconstruction flaps;
  • grafts;
  • penile or other genital replantation; and
  • other tissues in which arterial inflow is present but venous drainage is inadequate.

Systematic reviews describe medicinal leeches as an accepted temporary method for relieving postsurgical venous congestion when surgical revision is not possible, has failed, or cannot immediately restore adequate drainage.

Leech therapy has also been studied for conditions such as:

  • knee osteoarthritis;
  • thumb-joint osteoarthritis;
  • other pain syndromes;
  • venous disease; and
  • several traditional or complementary-medicine indications.

These uses should be distinguished from the FDA-cleared venous-congestion indication because their evidence and regulatory status are different.

  1. How does leech therapy work?

Modern leech therapy works through a combination of mechanical blood removal and biochemical effects.

While attached, the leech removes blood from congested tissue.

At the same time, its saliva introduces numerous biologically active substances that help it feed successfully. These include compounds that:

  • inhibit thrombin;
  • interfere with platelet adhesion and aggregation;
  • affect coagulation;
  • promote local blood flow; and
  • prevent the bite from sealing immediately.

The best-known salivary anticoagulant is hirudin, which directly inhibits thrombin.

Another important substance, calin, interferes with platelet adhesion to collagen and is thought to contribute to prolonged bleeding after the leech detaches.

Modern molecular studies have identified many additional leech salivary proteins and peptides, including eglins, bdellins, destabilase, saratin, and others.

For venous congestion, however, the clinically important effect is straightforward: remove stagnant blood and keep new blood draining from the congested area until venous circulation improves.

  1. Is leech therapy safe? What are the main risks?

Medicinal leech therapy can be extremely useful when properly performed, but it is not risk-free.

The two most important complications are:

  1. Infection

Medicinal leeches normally contain bacteria in their digestive tract, particularly species of Aeromonas. These organisms help the leech digest blood but can cause infection in human tissue.

  1. Blood loss

The therapeutic effect deliberately creates continued bleeding. When many leeches are used repeatedly over several days, blood loss can become substantial and may cause anemia or require transfusion.

Other reported complications include:

  • itching;
  • local irritation;
  • allergic reactions;
  • prolonged or excessive bleeding;
  • migration of a leech away from the intended site; and
  • rarely, other complications related to the underlying surgery or tissue condition.

Reviews of leech complications consistently identify infection and bleeding/anemia among the most important risks.

  1. Does leech therapy hurt?

The initial bite may produce a mild pinch, prick, or burning sensation, but experiences vary considerably.

It is often stated that leech saliva contains an anesthetic that “numbs” the bite. That explanation is not well established.

Leech saliva clearly contains substances that allow the animal to feed with relatively little disturbance from its host, and many patients report little discomfort. However, a specific clinically proven anesthetic or analgesic substance responsible for painless feeding has not been definitively identified.

During feeding, patients may feel:

  • mild pulling;
  • movement;
  • itching;
  • tingling; or
  • little sensation at all.

Pain should therefore be monitored rather than assumed to be absent.

  1. Who should not receive leech therapy?

Contraindications and precautions depend on the clinical situation, but particular concern applies to patients with:

  • severe anemia;
  • significant bleeding disorders;
  • uncontrolled coagulopathy;
  • severe thrombocytopenia;
  • inability to tolerate additional blood loss;
  • serious allergy to leeches or relevant treatment materials;
  • severe immune compromise in some circumstances; or
  • inability to receive appropriate antimicrobial prophylaxis when that is required.

Anticoagulant and antiplatelet medications require careful review because they may increase blood loss, although their presence is not necessarily an absolute contraindication in every surgical situation.

Pregnancy is often listed in traditional contraindication lists, but the evidence for an absolute pregnancy-specific prohibition is limited. In modern hospital use, the decision should be based on the patient’s clinical condition, bleeding risk, infection risk, urgency, and alternative treatments.

Because leech therapy is usually being considered to save threatened tissue, contraindications must be weighed against the potential consequence of losing the flap, graft, or replanted part.

  1. How is leech therapy performed?

The exact protocol depends on the surgical problem.

A clinician identifies the congested tissue and places one or more medicinal leeches on the appropriate area.

A leech may be guided to a particular site using gauze, a syringe barrel, or another positioning method.

Once attached, the leech feeds until it becomes engorged and usually detaches spontaneously.

Feeding commonly lasts roughly 20–45 minutes, although individual leeches may feed for longer.

After detachment, the site is generally allowed to continue oozing because this continued bleeding is an important part of the therapeutic effect.

Depending on the severity of the congestion, treatment may be repeated every few hours over several days while clinicians monitor:

  • tissue color;
  • capillary refill;
  • temperature;
  • swelling;
  • bleeding;
  • hemoglobin and hematocrit;
  • infection; and
  • evidence that natural venous drainage is improving.
  1. How much blood is lost, and can a patient need a transfusion?

A single leech directly removes only a relatively small amount of blood—often roughly 5–15 mL while feeding.

But that number seriously understates the total potential blood loss.

The bite may continue bleeding for hours after the leech falls off. When several leeches are applied repeatedly over a period of days, cumulative blood loss can become clinically significant.

In reconstructive-surgery series, anemia requiring transfusion is a well-recognized complication. A systematic review of leech therapy in breast surgery, for example, identified anemia requiring transfusion among the common complications.

Therefore, the draft’s comparison with a normal blood donation should be removed.

A single application may involve much less blood than a donation, whereas a prolonged course of leech therapy may eventually result in considerably greater cumulative blood loss.

For this reason, hospital protocols commonly include repeated blood counts and preparation for transfusion when necessary.

  1. Are medicinal leeches reused? Where do they come from?

Medicinal leeches used clinically should be treated as single-use biological medical devices.

After feeding on a patient, a leech contains that patient’s blood as well as its normal intestinal microorganisms. Reusing it could create a risk of transmitting bloodborne pathogens and other microorganisms.

FDA-cleared suppliers breed and maintain medicinal leeches under controlled conditions and provide instructions concerning their storage, handling, and disposal.

FDA documentation for one cleared medicinal-leech product specifically instructs that used leeches be euthanized and disposed of as potentially infectious biological waste.

They should never be transferred from one patient to another.

  1. How many treatments are needed, and what happens afterward?

There is no universal number.

For acute venous congestion, leeches may be applied repeatedly over several hours or several days.

The goal is not to complete a predetermined number of treatments. The goal is to support the tissue until:

  • venous circulation improves;
  • new small blood vessels develop;
  • surgical correction becomes possible;
  • the tissue is judged no longer salvageable; or
  • complications require stopping therapy.

After each application, the bite sites are covered with absorbent dressings while continued bleeding is monitored.

Clinicians also monitor:

  • hemoglobin;
  • signs of infection;
  • tissue viability;
  • local swelling;
  • blood pressure and symptoms of blood loss; and
  • response to antimicrobial prophylaxis.

For outpatient or off-label uses such as osteoarthritis, treatment schedules have varied substantially among studies.

  1. Are medicinal leeches FDA-approved?

The more precise term is FDA-cleared, not FDA-approved.

Several medicinal-leech products have received 510(k) clearance in the United States.

FDA’s current product classification states that medicinal leeches are indicated:

as an adjunct to graft-tissue healing when venous congestion may delay healing, or to overcome venous congestion by creating prolonged localized bleeding.

The original U.S. clearance for a medicinal-leech product was issued in 2004, with additional products subsequently cleared.

An important recent regulatory change occurred on December 30, 2024, when FDA transferred regulatory responsibility for medicinal leeches and medical maggots from the Center for Devices and Radiological Health (CDRH) to the Center for Biologics Evaluation and Research (CBER) because they are living organisms that more closely resemble products overseen by CBER.

Medicinal leeches remain regulated under the medical-device framework and product code NRN.

  1. How long does a typical application last?

A medicinal leech commonly remains attached for approximately 20–45 minutes, although feeding time varies.

A fully engorged leech usually detaches spontaneously.

The entire episode of care lasts much longer because preparation, application, monitoring, dressing changes, post-detachment bleeding, laboratory monitoring, and repeat treatments may continue for hours or days.

Thus, it is useful to distinguish a single leech feeding from the patient’s entire course of leech therapy.

  1. Why does the bite keep bleeding after the leech falls off?

Continued bleeding is intentional and is one of the main reasons leeches are useful for venous congestion.

The leech must prevent its blood meal from clotting while feeding. Its saliva therefore contains a combination of substances that interfere with hemostasis.

These include:

  • hirudin, which inhibits thrombin;
  • calin, which interferes with platelet adhesion to collagen;
  • platelet-aggregation inhibitors;
  • apyrase and related substances; and
  • additional anticoagulant and blood-flow-modifying compounds.

Calin in particular has been identified as a likely contributor to the prolonged post-bite bleeding phenomenon.

The bite may therefore ooze for several hours after detachment.

In venous-congestion treatment, this is beneficial because the small wound continues acting as a temporary route for blood to escape.

Excessive or prolonged bleeding, however, must be distinguished from the desired therapeutic bleeding and may require intervention.

  1. Can medicinal leeches cause infections?

Yes.

One of the most important facts about modern leech therapy is that medicinal leeches are not sterile animals.

Their digestive tract normally contains symbiotic bacteria, especially Aeromonas species. These bacteria help the leech process its blood meal.

Unfortunately, they can also cause human infection.

Leech-associated infections may include:

  • cellulitis;
  • wound infection;
  • flap or graft infection;
  • tissue necrosis;
  • bacteremia; and
  • occasionally severe systemic infection.

Studies and reviews consistently identify Aeromonas hydrophila, A. veronii, and related species as important pathogens associated with medicinal-leech therapy.

The fact that a medicinal leech comes from a controlled medical supplier therefore does not mean that its gut has been sterilized.

  1. How much does leech therapy cost, and is it covered by insurance?

There is no meaningful single price for medicinal leech therapy.

For the FDA-cleared indication, the cost of the actual leeches is often only a small part of the total expense.

Hospital treatment may also involve:

  • reconstructive or microsurgery;
  • prolonged hospitalization;
  • frequent nursing care;
  • antibiotics;
  • laboratory monitoring;
  • blood transfusions;
  • dressings; and
  • repeated surgical evaluation.

Coverage therefore depends much more on the patient’s hospitalization, surgery, diagnosis, medical necessity, and insurance policy than on a stand-alone “leech therapy fee.”

When leeches are used as part of medically necessary reconstructive care, the treatment may be incorporated into covered hospital care.

Off-label or complementary uses may be handled differently by insurers.

For that reason, I would remove the draft’s estimate that an outpatient treatment “can range from a few hundred dollars upward.” It is too variable to be particularly useful and may rapidly become outdated.

  1. What does the scientific evidence show for uses other than venous congestion?

The evidence varies greatly by condition.

The best studied non-surgical use is knee osteoarthritis.

Randomized trials have reported improvements in pain and function after periarticular medicinal-leech application. A 2014 systematic review found evidence supporting short-term improvement, and a later meta-analysis of four randomized trials involving 264 patients also found reductions in pain and improved function compared with control treatments.

However:

  • the studies were relatively small;
  • treatment methods varied;
  • blinding is difficult;
  • adverse effects were more frequent with leech therapy in some analyses; and
  • modern osteoarthritis treatment has many alternative therapies with much larger evidence bases.

Thus, knee osteoarthritis represents a promising but off-label application, not an FDA-cleared indication.

Evidence for many other traditional claims is much weaker.

A biologically active leech-saliva molecule or historical use should not by itself be interpreted as proof that whole-leech therapy is effective for a disease.

  1. Why are antibiotics often given during medicinal leech therapy?

Because the leech’s normal intestinal bacteria can infect the patient.

For reconstructive use, antimicrobial prophylaxis directed against Aeromonas species has long been recommended by many surgical programs.

This is not a minor theoretical concern: infection can compromise the same flap or replanted tissue that leech therapy is trying to save.

However, antibiotic selection has become more complicated.

Historically, fluoroquinolones such as ciprofloxacin were frequently used. Reports have since documented ciprofloxacin-resistant Aeromonas transmitted from medicinal leeches.

A 2021 review emphasized that prophylactic antibiotic choice should account for changing resistance patterns in leech-associated Aeromonas.

A 2024 analysis likewise examined antibiotic-resistant infections associated with hirudotherapy, reinforcing the importance of local susceptibility information and antimicrobial stewardship.

There is therefore no single antibiotic that should be presented in a general FAQ as universally appropriate.

The principle is more important:

clinicians should use an antimicrobial strategy active against the organisms associated with their medicinal-leech supply and adapt that strategy to local resistance patterns and patient factors.

  1. Is hirudin responsible for all of the therapeutic effect?

No.

Hirudin is the best-known leech salivary molecule and is a powerful direct thrombin inhibitor, but medicinal-leech feeding depends on a cocktail of bioactive substances.

These include compounds affecting:

  • thrombin;
  • platelet adhesion;
  • platelet aggregation;
  • inflammation;
  • extracellular matrix;
  • vascular responses; and
  • other aspects of blood feeding.

Modern molecular studies have identified well over 100 candidate proteins and peptides in leech secretions.

This also explains why administering a purified anticoagulant is not necessarily equivalent to applying a leech for venous congestion.

The leech provides both:

  1. physical removal of blood, and
  2. continued localized bleeding created by a mixture of salivary substances.

For reconstructive surgery, those effects together are what make the living organism useful.

  1. Are all “medicinal leeches” the same species?

No.

The name Hirudo medicinalis has historically been used broadly, but taxonomic work has shown that several closely related species have been used medicinally.

FDA-cleared products have included:

  • Hirudo medicinalis; and
  • Hirudo verbana.

In one FDA 510(k) submission, H. verbana was identified as the Southern European medicinal leech and H. medicinalis as the Northern European medicinal leech; the manufacturer described them as clinically equivalent for relief of venous congestion.

Other blood-feeding leech species are used medically in different parts of the world.

Species identity matters because different leeches may differ in:

  • salivary chemistry;
  • gut microbiota;
  • size and feeding behavior;
  • regulatory status; and
  • clinical evidence.

Therefore, a leech should not be considered suitable for medical use simply because it is capable of sucking blood.

Modern therapy should use appropriately sourced, identified, regulated medicinal leeches rather than wild-caught or aquarium leeches.

  1. What happens to the leech after treatment, and what about leech welfare?

A medicinal leech that has fed on a patient should not be reused.

It contains the patient’s blood, and reuse would create infection and bloodborne-pathogen risks.

FDA-cleared product instructions describe euthanizing used leeches and disposing of them as potentially infectious biological waste. One cleared product instructs immersion in at least 70% isopropyl alcohol followed by disposal through the appropriate biological-waste system.

That practice raises an ethical issue similar to those involving other living therapeutic organisms.

Medicinal leeches should be:

  • appropriately housed before use;
  • maintained at suitable temperatures;
  • kept in appropriate water;
  • protected from contamination;
  • handled gently;
  • not subjected to unnecessary injury or stress; and
  • euthanized humanely after use according to institutional and product protocols.

Unlike a reusable instrument, the individual leech is a living organism that becomes unusable after performing its therapeutic role.

Responsible hirudotherapy therefore requires attention to both patient welfare and animal welfare, while recognizing that infection-control requirements make reuse unsafe.

REFERENCES

Andereya, S., Stanzel, S., Maus, U., et al. (2008). Assessment of leech therapy for knee osteoarthritis: A randomized study. Acta Orthopaedica, 79(2), 235-243.
PubMed record

Brauer, P. R., Saadah, M., Fritz, M. A., Wu, S. S., & Lamarre, E. D. (2024). Analysis of antibiotic resistant infections associated with hirudotherapy. American Journal of Otolaryngology, 45(6), 104500.
PubMed record

Herlin, C., et al. (2017). Leech therapy in flap salvage: Systematic review and practical recommendations. Annales de Chirurgie Plastique Esthétique.
PubMed record

Koeppen, D., Aurich, M., & Rampp, T. (2014). Medicinal leech therapy in pain syndromes: A narrative review. Wiener Medizinische Wochenschrift, 164, 95-102.
PubMed record

Lauche, R., Cramer, H., Langhorst, J., & Dobos, G. (2014). A systematic review and meta-analysis of medical leech therapy for osteoarthritis of the knee. Clinical Journal of Pain, 30(1), 63-72. https://doi.org/10.1097/AJP.0b013e31828440ce.
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Mumcuoglu, K. Y. (2014). Recommendations for the use of leeches in reconstructive plastic surgery. Evidence-Based Complementary and Alternative Medicine.
[Useful clinical review for final bibliography expansion.]

Munro, R., Jones, C. P., & Sawyer, R. T. (1991). Calin – a platelet adhesion inhibitor from the saliva of the medicinal leech. Blood Coagulation & Fibrinolysis, 2(1), 179-184.
PubMed record

Sig, A. K., Guney, M., Uskudar Guclu, A., & Ozmen, E. (2017). Medicinal leech therapy – an overall perspective. Integrative Medicine Research, 6(4), 337-343. https://doi.org/10.1016/j.imr.2017.08.001.
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Free full text

U.S. Food and Drug Administration. (2004; current record). Medicinal Leeches, 510(k) BK251211 / former K040187.
FDA medicinal-leech clearance record

U.S. Food and Drug Administration. (2024). Transfer of regulatory responsibility from the Center for Devices and Radiological Health to the Center for Biologics Evaluation and Research: Medical maggots and medicinal leeches.
FDA regulatory-transfer information

U.S. Food and Drug Administration. (current). Product classification: Leeches, medicinal (NRN).
FDA product-classification record

Whitaker, I. S., Oboumarzouk, O., Rozen, W. M., et al. (2012). The efficacy of medicinal leeches in plastic and reconstructive surgery: A systematic review of 277 reported clinical cases. Microsurgery.

Whitaker, I. S., Izadi, D., Oliver, D. W., Monteath, G., & Butler, P. E. M. (2004). Hirudo medicinalis and the plastic surgeon. British Journal of Plastic Surgery.

Wollina, U., Heinig, B., Nowak, A., et al. (various). Clinical literature on medicinal-leech treatment and venous congestion.