Why have doctors used leeches since ancient times for hypertension and the threat of hemorrhage?

Hypertension is high blood pressure. With it, there is a risk of rupture of blood vessels (stroke) from the fact that excess blood presses on the vascular wall. Leeches suck out some of the blood during the bite, reducing its amount. An excess amount of blood stops pressing on the vessels, reducing the likelihood of vessel rupture. Also, a stroke can occur due to a blood clot – a blockage of a vessel. Leeches secrete hirudin during the bite. It is a substance that makes the blood thinner. Hirudin, getting into the blood, does not allow blood clots to form inside the vessels.