Known as Hirudo medicinalis, it was formerly employed for the abstraction of small quantities of blood in inflammatory and other conditions.

Leeches were used as a method of bloodletting, a practice common up to the middle of the 19th century.

In modern times, leeches have been used to evacuate periorbital hemorrhage (black eye) and to remove congested venous blood from the suture lines of re-implanted fingers.

Sometimes, a patient's veins are too weak to carry blood and it builds up, causing venous congestion and since leeches are a source of hirudin, an anticoagulating principle secreted by their buccal glands and leech saliva contains several active substances including inhibitors of platelet aggregation, they are used to decrease such venous congestion.

The leech's saliva contains substances that anesthetize the wound area, dilate the blood vessels to increase blood flow, and prevent the blood from clotting and so attaching leeches to the body draws the blood away gradually and painlessly.

Leeches are particularly useful in plastic surgery; such as, breast reconstruction and where a part of the body has become severed and had to be sewn back on.