The complete colon exam

Colonoscopy: what actually happens

A colonoscopy uses a flexible camera to inspect the colon and rectum. Unlike noninvasive screening tests, it can also biopsy tissue and remove many polyps during the same procedure.

Go to the prep center Understand results

Planning

Your team reviews why the colonoscopy is being done, health conditions, medications, prior prep quality, transportation, and sedation plan.

Bowel prep

You follow a prescribed diet and bowel-cleansing regimen. A clean colon is essential because residual stool can hide lesions.

Check-in

Staff confirm medications, allergies, vital signs, consent, and your discharge/escort plan. Sedation is commonly used in the United States.

Exam

The colonoscope is advanced through the rectum and colon. The clinician inspects the lining, can take biopsies, and can remove many polyps.

Recovery

You recover from sedation and receive instructions. If sedation was used, driving and major decisions are generally restricted for the rest of the day according to the facility’s instructions.

Final results

Visual findings may be discussed immediately. Pathology from removed tissue can take longer, and the next interval depends on the full report.

What colonoscopy can do

One procedure can both find and treat many precancerous lesions.

Inspect

Directly examines the colon lining rather than inferring risk from stool or blood markers.

Biopsy

Tissue samples can be taken from an abnormal area for microscopic examination.

Remove

Many polyps can be removed during the same procedure, which is one reason colonoscopy can help prevent colorectal cancer.

Safety

What are the important risks?

Serious complications are uncommon, but colonoscopy is an invasive procedure. Individual risk changes with age, medical conditions, medications, sedation, and whether a biopsy or polyp removal is performed.

Bleeding

Bleeding can occur after biopsy or polyp removal. Some bleeding may be delayed.

Perforation

A tear in the colon wall is uncommon but potentially serious and may require hospitalization or surgery.

Sedation-related problems

Breathing, blood pressure, heart rhythm, or medication reactions can occur, which is why monitoring is used.

Incomplete or inadequate exam

Poor bowel cleansing, anatomy, or technical factors can limit the examination and may lead to earlier repeat testing.

After colonoscopy: Follow your discharge instructions. Seek prompt medical advice for severe or worsening abdominal pain, fever, significant or persistent bleeding, repeated vomiting, fainting, breathing difficulty, or other symptoms your procedure team identifies as urgent.

Ask before the procedure

A useful question list

What prep am I using, and exactly when do I take each dose? Which medications need special instructions? What should I do with blood thinners, diabetes medicines, insulin, or GLP-1 medications? When must I stop solid food and clear liquids? What type of sedation is planned? Who must drive or accompany me home? How and when will I receive pathology results? Whom do I call after hours if I have a problem?

Do not change prescription medicines based on this website. Medication management around colonoscopy should come from the prescribing clinician and procedure team.

Evidence

Primary sources for this page

ASGEPatient information: understanding colonoscopy AGA / U.S. Multi-Society Task Force2025 bowel preparation quality guidance NCIColorectal cancer screening information

Medical content reviewed against these sources on September 5, 2026. This does not replace clinician review before public launch.