The information provided here is not a replacement for a doctor. You shouldn't use it for the purpose of self-diagnosing or self-medicating but rather so you can have a more informed discussion with a professional TCM practitioner.
Because it is a herb specifically indicated to treat loss of blood as can be seen on Cuttlebone's page.
Its main actions are: Restrains and stops bleeding. Holds Essences and stops seminal discharge or leukorrhea. Clears Dampness and promotes wound heeling. Inhibit gastric secretion and stops pain.