One of the primary dangers associated with a colonoscopy is a potential adverse reaction to the sedation used before the procedure, explains Mayo Clinic. People may also experience a significant amount of bleeding where the polyp or tissue sample was taken.
The overall risk of complications during a standard colonoscopy is just 0.35 percent, according to Amber J. Tresca for About.com. The risk of complication goes up to 2.3 percent when a polyp is removed. A perforation in the colon or rectum wall is another significant danger with the procedure, reports Mayo Clinic. Additional dangers include postpolypectomy syndrome and infections that may develop afterward.