If you had any drug that has iron in it this can result in diarrhoea
and black stools or if you have any leafy vegetable it can result in greenish stools. tarry black stool indicate some internal haemorrhage it can be from ulcer or any other lession or cause.
Stop all medicines if taking any . Amongst herbal combinations that we use to hasten clot formation and check bleeding is Bol Badh ras 2 tablets. bd.