Rakthamoksham (Leech Therapy) Leeches produce an enzyme in their saliva called hirudin. Hirudin is a powerful anticoagulant. They produce this to prevent their host from forming a clot so that they can feast on blood more easily. When you apply a leech, the hirudin acts locally at the bite site to allow continued bleeding for 2-3 hours after the leech is removed. While attached, the leech actively removes some of the built up blood which eases the pressure within the tissue.
After the leech is removed, the built up venous blood will continue to drain from the site where the leech was attached, which is therapeutic for the tissue. The effects of the hirudin may last up to a few hours. You can tell that it's no longer active when the blood stops draining.
Widen the vessels, thus causing inflow of blood to the site
It also has a thrombolytic effect, which can also dissolve clots of blood that have formed
The anti-clotting agents also dissolve clots found in the vessels, eliminating the risk of them traveling to other parts of the body and blocking an artery or vein
Effectively inhibiting coagulation of the blood