Colonoscopy Risks

Going for your first colonoscopy? This lets a doctor check your colon and rectum for cancer and polyps -- growths that can be early signs of cancer. It saves lives, so if your doctor suggests you get one, be sure you do.

It’s a fairly safe exam. On average, two serious complications occur for every 1,000 procedures performed. But it’s not without risks. Here are four you should talk to your doctor about.

Abdominal Discomfort or Pain

This is the most common side effect of colonoscopy. You might feel cramping or bloating afterward.

Your doctor will use a long, flexible tube called a colonoscope to look inside your colon. It has a light and camera to help her see what’s going on in there. She may also insert air inside your colon to get a better view. She might use water or a suction device as well as certain surgical tools if she needs to remove a polyp. All these things can move and stretch your colon, so you might feel uncomfortable for a day or two after the exam. You may also feel nauseous and might even throw up. These symptoms usually aren’t dangerous, but if you have vomited or are in pain, call your doctor right away.


You could notice blood from your rectum or in your stool after a colonoscopy. Most of the time, this happens because your doctor had to take a tissue sample or remove a polyp from your colon. Call your doctor right away if it continues or if there’s a lot of blood. Certain medications, such as vitamins and over-the-counter painkillers like aspirin, can increase your risk of bleeding. If you take them, be sure to tell your doctor before you go in for your procedure.

A Bad Reaction to Anesthesia

You’ll be asleep during your exam, so you won’t feel anything. You may feel woozy or shaky when you wake up. In rare cases, some people can have serious reactions to the medications such as heart or breathing problems. But your doctor and her team are trained to identify and treat these side effects. Tell her if you’re allergic to any medicines or have ever had a bad reaction to anesthesia.


A Tear in the Colon or Rectum Wall

The tool used during colonoscopy could push too hard against your colon. This can cause a small tear. If it does, your doctor may need to repair it with surgery. Fortunately, this is rare.

When to Seek Help

Call your doctor right away if you have any of these symptoms after your screening:

  • Severe pain or cramping in the abdomen
  • A hard belly
  • You can’t pass any gas or stool
  • Fever
  • Dizziness
  • Vomiting
  • Frequent or severe bloody bowel movements
  • Severe or on-going bleeding from your anus


WebMD Medical Reference Reviewed by Nayana Ambardekar, MD on December 07, 2017



American Cancer Society: "Frequently Asked Questions About Colonoscopy and Sigmoidoscopy."

National Institute of Diabetes and Digestive and Kidney Diseases: "Colonoscopy."

American Society for Gastrointestinal Endoscopy: "Complications of colonoscopy."

Johns Hopkins Medicine: "Colonoscopy."

Roberto Bergamaschi, MD, PhD, Chief of the Division of Colon & Rectal Surgery at Stony Brook University School of Medicine.

Kavic, S., Surgical Treatment, published online 2001.

UptoDate: "Colonoscopy (Beyond the Basics)."

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