The possible complications from a colonoscopy include tearing of the rectum wall or colon, known as a perforation; bleeding from the site of polyp or anomalous tissue removal; and an adverse response to the sedative, according to Mayo Clinic. The benefits for cancer prevention outweigh the risks for many patients.
Perforation of the bowel means that a hole has formed all the way through. An error in manipulating the surgical devices during polyp removal as part of the colonoscopy can cause this, although it is also a risk in older colonoscopy patients because of the fragility of the tissue. When this happens, the contents of the colon can spill out into the abdominal cavity. This leads to inflammation on the membrane lining the cavity, and this is an emergency necessitating immediate treatment, as stated by Healthline.
The other two complications are not as potentially dangerous for the patient. In general, the benefits of colonoscopy procedures in terms of screening for cancer make the risks worthwhile. A study released in January 2011 found that colonoscopies save lives by helping doctors find and remove polyps before they can develop into malignant cancers in the colon. Yearly, over a million people worldwide receive a colorectal cancer diagnosis, and the disease kills more than half of them, states WebMD.