The bleeding rate of both EGD (including biopsy) and colonoscopy (including biopsy, cold or hot snare polypectomy, or EMR) in patients who continue to take various antithrombotic drugs is studied prospectively. The immediate or delayed bleeding that requires hemostatic clipping or other endoscopic treatments is defined as the bleeding. Immediate bleeding requiring hemostatic clipping is defined as spurting or oozing which continued for more than 30 seconds. Delayed bleeding is defined as bleeding that requires the endoscopic treatment within 2 weeks after endoscopy. Prophylactic clipping is not performed after taking biopsy and doing polypectomy. Additionally, investigators evaluate the rate of injured submucosal arteries of the excised specimen when the bleeding occurs.