Is it common to have blood in the stool during period?

No!: It is always abnormal to have blood in the stool and should be evaluated by your physician. Sometimes, it may appear as if blood is in the stool when there is a lot of menstrual blood in the area. There is one condition, endometriosis, that can cause bleeding in the stool during periods. Women with this condition often have very severe menstrual cramps.