What are the possible side effects of a colonoscopy?

Daniel Labow, MD
Surgical Oncology

Colonoscopy is a very safe procedure overall. Bloating and some mild discomfort is possible the day of the test. You might feel groggy for a few hours after the test. There is a small risk of bleeding and also a very small risk (<0.5%) of colon perforation, which could require urgent surgery.

The bowel preparation before a colonoscopy can be unpleasant. The test itself may be uncomfortable, but the sedative usually helps with this, and most people feel normal once the effects of the sedative wear off. Some people may have gas pains or cramping for a while after the test.
In some cases, people may have low blood pressure or changes in heart rhythms due to the sedation during the test, although these are rarely serious.
If a polyp is removed or a biopsy is done during the colonoscopy, you may notice some blood in your stool for a day or 2 after the test. Significant bleeding is slightly more likely with colonoscopy than with sigmoidoscopy, but it is still uncommon. In rare cases, continued bleeding might require treatment.
Colonoscopy is a safe procedure, but on rare occasions the colonoscope can puncture the wall of the colon or rectum. This is called a perforation. It can be a serious complication and may require surgical repair. Talk to your doctor about the risk of this complication.
Here are some potential risks and complications of a colonoscopy procedure: 
  • Some people have cramps and abdominal swelling. This is caused by
          the air used to inflate the colon, and passes shortly after the
  • If your doctor takes a biopsy, you may see small amounts of blood in
          your stool after the procedure. If there’s a lot of blood, you may
          need another colonoscopy, or possibly surgery.
  • There is a slight risk (1 in 3,000) of perforating the colon. This may
          cause bleeding or infection. If this occurs, you may need immediate
          surgery to repair the injury.
  • If the colon and rectum were difficult to examine or not completely
          empty, the procedure may not detect some problems.    
  • As with any medicine, there’s a slight chance you may have a reaction
          to the sedative.
Mark E. Chisam, MD
Radiation Oncology

Colonoscopy usually takes 30 to 60 minutes. Cramping or bloating may occur during the first hour after the procedure. It can take 1 to 2 hours for the sedative to completely wear off. Full recovery is expected by the next day. Rare side effects can occur and include: 

  • severe abdominal pain
  • fever
  • bloody bowel movements
  • dizziness
  • weakness

If any of these symptoms were to develop, you should contact your doctor immediately

Ajay K. Sahajpal, MD
Transplant Surgery
As with any medical procedure, there are side effects. The most significant side effect is a perforation of the colon. This can range from a small perforation that can be managed without surgery to a major perforation and leakage requiring surgery to repair. The other major side effect is bleeding, especially if a biopsy is done or polyp removed. Of note, both of these are rare occurences. There are also side effects associated with the use of sedation for the procedure.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.