 [ Symptoms ] my stool is jet black i have had this before how long does it take for the stomach to digest and pass blood from an ulcer i have got a lengthy history of bleeding gi is which has resulted in multiple hospitalizations for a week or more at a time each time requiring transfusions from anywhere to 9+ and sometimes up to 14 units of blood even though i just noticed it i am already growing weak and getting out of breath for no apparent reason something that never happened this soon before so i was wondering if i have been bleeding in my stomach for a long time and it is just now being expelled [ Disease ] you need to get to the er now with your medical history it is not that important when you started bleeding but rather how much you are bleeding right now a rapid bleed in the stomach could cause black stools relatively fast because you are weak and out of breath it would not be wise to delay an immediate medical evaluation