以下取自維基百科
1. 黑便為血紅素被消化性酵素或腸內菌改變所造成
Melena or melaena refers to the dark black, tarry feces that are associated with upper gastrointestinal bleeding.The black color and characteristic strong odor are caused by hemoglobin in the blood being altered by digestive enzymes and intestinal bacteria.
2. 最常造成黑便的原因為潰瘍疾病
The most common cause of melena is peptic ulcer disease.[5] However, any bleeding within the upper gastrointestinal tract or the ascending colon can lead to melena.