A colonoscopy is a screening and diagnostic test that lets a doctor examine the entire lining of your colon and rectum using a long, thin, flexible tube with a camera on the end. The procedure typically takes 30 to 60 minutes and is the most thorough way to detect precancerous polyps and colorectal cancer. If the doctor spots a polyp during the exam, they can remove it on the spot, often preventing cancer before it ever develops.
What a Colonoscopy Detects
Colorectal cancer almost always starts as small, abnormal growths called polyps on the inner wall of the colon or rectum. Most polyps are harmless at first, but some slowly turn cancerous over a period of years. A colonoscopy catches these growths while they’re still precancerous, which is why it’s considered the gold standard for colorectal cancer screening. Finding and removing polyps during the procedure effectively resets your risk.
Beyond cancer screening, a colonoscopy is used to investigate symptoms like unexplained rectal bleeding, chronic diarrhea, abdominal pain, or sudden changes in bowel habits. It’s also a key tool for diagnosing and monitoring inflammatory bowel diseases like Crohn’s disease and ulcerative colitis. If a different, less invasive screening test (like a stool-based test) comes back positive, a colonoscopy is the standard follow-up to get a direct look inside.
When and How Often You Need One
The U.S. Preventive Services Task Force recommends colorectal cancer screening for all adults aged 45 to 75 who are at average risk. “Average risk” means no prior polyps, no inflammatory bowel disease, and no family history of genetic conditions like Lynch syndrome that sharply raise colorectal cancer risk. If you fall into one of those higher-risk categories, your doctor will likely recommend starting earlier or screening more frequently.
For average-risk adults, a colonoscopy is recommended once every 10 years. That long interval reflects how slowly most polyps develop into cancer. If polyps are found and removed, you’ll typically be asked to come back sooner, often in 3 to 5 years, depending on the number, size, and type of polyps.
How to Prepare
The preparation is the part most people dread, and it does require commitment. The goal is to completely empty your colon so the doctor has a clear view. Prep protocols vary, but a common approach involves about two days of dietary restrictions combined with a laxative solution.
Starting two days before the procedure, you switch to clear liquids only: things like broth, sports drinks, black coffee or tea, gelatin, popsicles, and clear juices without pulp. No solid foods. In the afternoon, you take laxative tablets followed by a large volume of laxative solution mixed into a sports drink, finishing the mixture within about an hour. This same pattern repeats the day before the test, and you drink a final round of the solution on the morning of the procedure, typically about five hours before you leave for your appointment.
The laxatives work quickly, so plan to stay near a bathroom. Most people find the prep uncomfortable but manageable. Drinking the solution cold and using a straw can make it easier to get down. The cleaner your colon, the better the doctor can see, so cutting corners on the prep can mean a repeat procedure.
What Happens During the Procedure
You’ll change into a hospital gown and lie on your side on an exam table. A nurse places an IV line in your arm to deliver sedation. Most colonoscopies use moderate to deep sedation given through the vein, which puts you in a drowsy, relaxed state. You likely won’t remember the procedure afterward. In some cases, general anesthesia is used based on individual factors.
Once you’re sedated, the doctor inserts the colonoscope (a flexible tube about the width of a finger) through the rectum and slowly advances it through the entire length of the colon. The camera sends a live image to a monitor, allowing the doctor to inspect the colon lining in detail. Air or carbon dioxide is gently pumped in to inflate the colon and improve visibility. The whole process usually wraps up in 30 to 60 minutes.
How Polyps Are Removed
If the doctor spots a polyp, they remove it immediately using small instruments passed through the colonoscope. Tiny polyps are grabbed with surgical forceps. Larger ones are scraped off with a wire loop called a snare, which can be heated or cooled to help cut and seal the tissue. After the polyp is detached, the doctor may use an electrocautery device to burn away any remaining tissue and seal the wound to prevent bleeding.
All removed polyps are sent to a lab for analysis. Results typically come back in one to two weeks, and they’ll tell you whether the polyp was benign, precancerous, or (rarely) cancerous. Your follow-up screening schedule depends largely on what the lab finds.
Recovery and What to Expect After
You’ll spend 30 minutes to an hour in a recovery area as the sedation wears off. Because the sedation affects your judgment and reaction time for the rest of the day, you cannot drive yourself home. Arrange for someone to pick you up before your appointment.
Bloating, gas, and mild cramping are normal afterward, caused by the air pumped into your colon during the exam. These symptoms usually pass within a few hours. You may also notice a small amount of blood in your first bowel movement if polyps were removed.
For the first 24 hours, stick to soft, bland, easy-to-digest foods: white toast, mashed potatoes, scrambled eggs, bananas, broth, yogurt, baked chicken, or white fish. Avoid red meat, raw vegetables, nuts, seeds, whole grains, spicy food, fried food, and dairy products like milk and ice cream, all of which can irritate your digestive system while it recovers. Drink more fluids than usual, focusing on water, herbal tea, juice, and electrolyte drinks. Most people return to their normal diet by the next day.
Risks and Complications
Colonoscopy is a very safe procedure, but like any medical test, it carries small risks. The two main complications are bleeding and perforation (a tiny tear in the colon wall). In a large pooled analysis of real-world outcomes, the rate of bleeding serious enough to require hospitalization was about 1.6 per 1,000 procedures. Perforation was even rarer, occurring in roughly 0.85 per 1,000 procedures. The risk of death was approximately 1 in 14,000. These risks are slightly higher when polyps are removed compared to a purely diagnostic exam, but they remain very low overall.
Reactions to the sedation, such as breathing or heart rate changes, are monitored throughout the procedure and are uncommon. Signs of a complication to watch for at home include severe abdominal pain, fever, heavy rectal bleeding, or dizziness. These are rare but need prompt medical attention.
Cost and Insurance Coverage
How much you pay depends on whether the colonoscopy is classified as a screening (no symptoms, routine check) or diagnostic (investigating symptoms or following up on an abnormal test). Under the Affordable Care Act, most private insurance plans cover screening colonoscopies with no out-of-pocket cost for average-risk adults starting at age 45. Medicare similarly covers screening colonoscopies at no cost every 10 years for average-risk individuals, or every 24 months for those at high risk.
There’s an important wrinkle, though. If your doctor finds and removes a polyp during what started as a screening colonoscopy, your cost-sharing can change. Under Medicare, polyp removal during a screening triggers a 15% coinsurance for both the provider’s services and the facility fee. Private insurance policies vary on this point, so it’s worth checking your plan’s details ahead of time. A diagnostic colonoscopy ordered because of symptoms or a positive stool test is typically subject to your plan’s standard deductible and copay structure, which can mean higher out-of-pocket costs.