Hirudotherapy is the oldest method of treatment with leeches. The therapeutic effect of leeches is determined by the properties of salivary gland secretions, which enter the human body after biting the leech skin. Saliva has analgesic, anti-inflammatory and vasodilating properties. This improves blood supply to tissues, improves the quality of oxygen delivery to organs and other nutrients, activates the growth of small capillaries and processes of nerve cells.