Medically Reviewed by Jabeen Begum, MD on May 17, 2024
11 min read

A colonoscopy is a medical procedure. A doctor inserts a camera mounted on long, flexible tube called a colonoscope into your rectum and colon. Colonoscopies are done to prevent, treat, and monitor diseases of your large intestine, such as colorectal cancer. Your colonoscopy will likely be done by a gastroenterologist or a colorectal surgeon, who both specialize in gastrointestinal disease.

Which diseases can be detected by a colonoscopy?

A colonoscopy can detect a number of different diseases, including:

  • Colorectal cancer
  • Colorectal polyps, or small growths that may turn into cancer but are typically harmless
  • Inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease
  • Intestinal ischemia, which causes reduced blood flow to your intestines
  • Diverticulosis, a condition that causes small pouches to form on the lining of your intestines
  • Diverticulitis, or inflammation of the pouches formed by diverticulosis
  • Ulcers
  • Gastrointestinal (GI) perforations, or holes in your GI tract
  • Large bowel obstructions

Colonoscopy age

When used to screen for colorectal cancer, your doctor likely will recommend you have your first at age 45. But certain risk factors may require you to get screened at a younger age. These include:

  • A personal or family history of colorectal cancer or certain types of polyps
  • A family history of hereditary colorectal cancer syndrome, such as familial adenomatous polyposis (FAP) or Lynch syndrome (also known as hereditary non-polyposis colon cancer, or HNPCC)
  • If you have an inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease
  • If you had radiation treatment for certain types of cancer in your abdomen or pelvis

Talk to your doctor about earlier screening if you have a family history of colorectal cancer. The number of young people with the disease has risen in recent years, and they’re often diagnosed when the disease has advanced and become more difficult to treat.

Colonoscopy cost

Federal law requires private insurance companies and Medicare to cover all costs related to colorectal cancer screenings. Medicaid coverage varies from state to state. If you are paying out of pocket, the national average cost of a colonoscopy for colorectal cancer screening is around $2,750. However, the cost can vary dramatically depending on factors like the type of health care facility where you have your procedure done and where you live. For example, in New Hampshire, the average cost if you have no insurance is $5,298. Programs like ColonoscopyAssist may be able to help you cover the cost if you have no insurance. Colonoscopies for reasons other than colorectal cancer screening may have different costs and coverage.

Before a colonoscopy, let your doctor know about any medications you take, including over-the-counter medications and supplements, as well as any conditions you have, including the following:

  • Pregnancy
  • Lung conditions
  • Heart conditions
  • Bleeding disorders
  • Allergies to any medications

If you take diabetes medications or medicines that affect blood clotting, your doctor might make adjustments to these a few days before your colonoscopy.  

Never stop taking any medication without first consulting your doctor.

If you take an iron supplement, you should stop 7 days before your colonoscopy.


Your doctor will provide you with detailed instructions on how to prepare for your colonoscopy. It’s very important that you follow these instructions closely. They will ensure that your colon is clean so that your doctor has a clear view of everything. If your colon is not fully clean, you may need to reschedule your procedure. Your doctor's instructions may be slightly different, but here’s what you usually will need to do in the days before your colonoscopy:

  • Eat a low-fiber diet for at least 2 to 3 days before your procedure. Do not eat seeds, nuts, popcorn, or other high-fiber foods.
  • Consume only a clear liquid diet on the final day before your colonoscopy. That means no solid food for breakfast, lunch, or dinner, or at any other time of the day.
  • You may have clear broth or bouillon, Jell-O, and ice pops (yellow, green, or clear).
  • Take the laxative your doctor provided as directed the afternoon or evening before your procedure (expect to spend a lot of time on the toilet).

The laxative (or laxatives, as you may be given more than one) you take is part of what’s called a bowel prep kit. That kit also contains electrolytes, sometimes mixed in with the laxative. Along with drinking a lot of fluids to stay hydrated, you need the electrolytes to help your body function properly. The laxative will make you poop A LOT, so you’ll lose significant amounts of water and electrolytes that you need to replace.

There are two main types of bowel prep kit.

Polymer-based formulas (PEG)

The more commonly used of the two, PEG kits are very effective and safe. However, they require you to drink lots of liquid laxative formula, in some cases more than a gallon. Some people find this challenging.

Saline-based formulas (NaP)

These come in pill form, which you may prefer. However, they can irritate your stomach if you have an inflammatory bowel disease. They also can upset your electrolyte balance, which is risky for people with certain conditions, like liver disease, kidney disease, various heart conditions, inflammatory bowel disease, diabetes, and more.

On the day before your colonoscopy, drink plenty of fluids. On the approved list:

  • Water
  • Broth
  • Apple juice
  • White grape or white cranberry juice
  • Ginger ale and Sprite (diet or regular)
  • Coffee and tea, with no milk or cream

Do not drink alcohol. Do not consume any red, blue, or purple food or drinks.

Make sure you arrange for a driver to bring you home after the colonoscopy. Because you receive sedating medication during the procedure, it is unsafe for you to drive or operate machinery for 8 hours after the procedure. Let your driver know you’ll be ready to go home 2 to 3 hours after you arrive for your colonoscopy.

Before your procedure, you’ll be given either general anesthesia or a sedative that will make you mostly unaware of what’s going on. 

Colonoscopy procedure

During your colonoscopy, you will lie on your side with your knees tucked up towards your chest. Your doctor will insert a colonoscope into your rectum. This is a long, flexible tube mounted with a light and a camera. The camera transmits real-time video to a screen that the doctor can view. As the scope moves through your colon, your doctor will watch for anything abnormal. Once the scope reaches the end of your colon, your doctor will slowly pull it back. That provides an opportunity for a second look to be sure nothing was missed.

Does a colonoscopy hurt?

An intravenous (IV) line will be inserted into one of your veins in order to deliver sedatives and pain medications. That way, you won’t feel any pain during your colonoscopy. You may feel some pressure as the colonoscope moves through your colon and as it’s used to inflate your colon to give your doctor a better view.

How long does a colonoscopy take?

The procedure takes about 30 minutes if your doctor finds nothing abnormal. However, it’s not uncommon to find small growths called polyps. While these rarely present any risk of being or becoming cancerous, your doctor likely will remove them. That can be done during your colonoscopy. It will add about 15 minutes to the total time required for the procedure. 

If your doctor sees anything suspicious that could be a sign of cancer, the colonoscope can be used to remove a tissue sample for analysis in a lab. This is called a biopsy. Your colonoscopy may take up to 60 minutes if it involves removing samples.

After your colonoscopy, you will stay in a recovery room for an hour for observation to make sure you don’t have any immediate complications. This also gives you time to fully wake up from the anesthesia. It will take up to 24 hours for it to fully wear off. That’s why you need someone to drive you home.

Colonoscopy side effects

You may feel some minor side effects after the procedure, including:

  • Gas, cramping, bloating, or nausea can occur in the first hour or so after your colonoscopy.
  • If you underwent general anesthesia, you may feel groggy and somewhat confused when you wake up. You could experience nausea or vomiting, dry mouth, chills, or a sore throat.
  • You may have minor bleeding after your first bowel movement following your colonoscopy. This may last a few days if you had any tissue removed.

Colonoscopy aftercare

Mostly, this involves taking it easy. The aftereffects of the anesthetic can last up to a day, so don’t drive, make important decisions, or return to work right away. You can resume your normal diet as soon as you feel ready.

If you feel bloated or gassy after your colonoscopy, walking can help you feel better.

Keep track of any bleeding. It’s normal to have some after your first bowel movement -- or longer if you had tissue removed -- but you should call your doctor if the bleeding continues. You should also call your doctor if your bleeding is significant or if you pass large clumps or clots of blood when you poop. 

Other signs that you should call your doctor: if you develop abdominal pain, a fever, or dizziness. This is uncommon, but it can happen, either right after your procedure or in the next few days.

Your doctor will give you instructions before you are discharged. Read them carefully and be sure to follow them. 

Your doctor may recommend that you eat foods that are easy on your stomach. That means avoiding high-fiber foods and going easy on dairy. This diet might include:

  • Sports drinks with electrolytes
  • Fruit juice
  • Herbal tea
  • Crackers
  • Soup, like chicken noodle or broth
  • Scrambled eggs
  • Canned fruit
  • Yogurt
  • Toasted white bread
  • Mashed potatoes

Foods to avoid include:

  • Alcohol
  • Whole grains
  • Tough, hard to digest meats like steak
  • Breaded and fried foods
  • Strongly spiced foods
  • Uncooked vegetables
  • Nuts and seeds

Colonoscopy complications

Most colonoscopies happen without problems, but complications, while rare, are possible. They include:

  • Tears or other injury to your colon wall
  • Bleeding that won’t stop after tissue removal
  • Infection
  • A bad reaction to the anesthetic

Read your discharge instructions carefully. Certain medications, such as blood-thinning agents, may need to be avoided temporarily if biopsies were taken or polyps were removed.

Before you go home, your doctor will review the procedure with you and let you know what, if anything, they found. If you had polyps or other tissue removed for analysis, the results won’t be ready right away. Your doctor can tell you when to expect a report.

Positive result

Your colonoscopy is positive if your doctor finds any polyps or abnormal tissue. Remember, though, most polyps are benign, not cancerous. However, they need to be removed and analyzed to be certain.

Normally, you won’t need another colonoscopy for 10 years. Finding polyps may lead your doctor to recommend that you have one sooner. This will depend on certain factors:

  • You have more than two polyps.
  • You have one or more large polyps, meaning it’s 0.4 inches (1 cm) or larger.
  • You have polyps and your colon was not clean enough to fully examine.
  • You have polyps that indicate a higher risk of cancer.
  • You have cancerous polyps.

You may need another colonoscopy if your doctor was not able to remove all the polyps or collect a tissue sample.

Negative result

This is what you want. It means your doctor found nothing of concern during your colonoscopy. You won’t need another colonoscopy for 10 years if you have a normal risk of colorectal cancer or have only small polyps in your colon. However, your doctor will recommend you have a colonoscopy sooner -- within 1 to 7 years -- if:

  • You had polyps removed that were a certain size or type or greater than a certain number of polyps.
  • You had polyps in a previous colonoscopy.
  • You have a genetic condition that raises your risk of colorectal cancer, such as Lynch syndrome.
  • You have a family history of colon cancer.

You may need to repeat your procedure if your doctor could not get a complete view of your colon because it was not fully clean.

Colonoscopy is considered the gold standard for detecting and treating early colorectal cancer. However, there are alternatives available that you and your doctor can discuss.

Virtual colonoscopy

This uses an imaging technique called computed tomography (CT) to take pictures of your colon from outside your body. You prepare the same way as for a standard colonoscopy so that your colon is as clean as possible before the exam. 

During the exam, you’ll lie on a bed that slowly moves into a scanning chamber and then out again about 15 minutes later. The entire procedure takes an hour or so. You won’t need to have anesthesia or sedatives

Fecal occult blood tests

For this test, you provide a small poop sample for analysis. If the lab finds blood in your poop, that could be a sign of cancer or another disease. However, this test can’t diagnose disease. It only tells your doctor that something is causing abnormal bleeding. If the test result is positive, meaning blood has been detected, you will need to undergo a colonoscopy to determine what’s causing it.

A colonoscopy can detect, prevent, and treat colorectal cancer. It’s also used for other conditions, such as inflammatory bowel diseases. Yes, it requires burdensome preparation, but it can be lifesaving. Talk to your doctor about when you should have a colonoscopy.

Do they put you to sleep for a colonoscopy?

Sometimes. You and your doctor will discuss your options before the procedure. You will either have general anesthesia, in which you’ll be unconscious, or you will remain awake but sedated.

Who performs a colonoscopy?

Most colonoscopies are performed by a gastroenterologist or a colorectal surgeon.

How long does it take to recover from a colonoscopy?

You’ll be able to go home about an hour after your procedure. However, give yourself 24 hours to fully recover and to allow the anesthetic to wear off completely. During that time, don’t drive, don’t make important decisions, and don’t return to work.

When do you get the results?

If your colon has nothing suspicious that needs to be removed and analyzed in a lab, your doctor will be able to tell you right away that your results are negative. That’s what you want to hear. If your doctor removes any polyps or other tissue for analysis, the results will be ready in a few days or weeks. Keep in mind that most polyps are benign and do not mean you have cancer.