A colonoscopy is a 30- to 60-minute exam where a doctor uses a flexible, camera-tipped tube to inspect the entire lining of your colon and rectum. The procedure itself is the shortest part of the experience. Most of the work happens beforehand, during a bowel preparation that clears your colon so the camera can get a clear view. Here’s what to expect at each stage.
Who Needs a Colonoscopy and When
The U.S. Preventive Services Task Force recommends colorectal cancer screening starting at age 45 for adults at average risk, continuing through age 75. Before 2021, the starting age was 50, but rising rates of colorectal cancer in younger adults prompted the change. If you have a family history of colorectal cancer, inflammatory bowel disease, or a genetic condition like Lynch syndrome, your doctor will likely recommend starting earlier.
Bowel Preparation: The Day Before
The prep is the part most people dread, and it’s also the most important. A clean colon lets the doctor spot even small polyps. A poorly prepped colon can mean repeating the whole process.
The day before your colonoscopy, you’ll switch to a clear liquid diet from the moment you wake up. That means broth, clear juice (no pulp), gelatin, water, tea, and coffee without milk or cream. No solid food at all. In the evening, typically between 5 and 8 p.m., you’ll drink the first dose of a prescription laxative solution. The most common type comes in a large jug: you drink a full glass every 10 to 15 minutes until half the jug (about two liters) is gone. This takes roughly an hour and a half to two hours. Other formulations come in smaller, more concentrated doses with instructions to follow them with a set amount of clear liquid.
The second dose happens early the next morning, often several hours before your appointment. This “split-dose” approach is standard because it produces a cleaner colon than drinking the full prep the night before. If your colonoscopy is scheduled early in the morning, you may need to set an alarm to get up and finish. The laxative works fast. Expect frequent, watery bowel movements within an hour of your first dose, so plan to stay close to a bathroom for the rest of the evening.
Arriving at the Facility
You’ll check in and change into a hospital gown. A nurse will place an IV line in your arm or hand, take your vital signs, and review your medical history and any medications you’re on. You’ll also confirm that you have someone to drive you home afterward, since sedation makes it unsafe to drive for the rest of the day. This check-in process typically takes 30 to 45 minutes.
Sedation Options
Most colonoscopies are performed under some level of sedation. There are a few tiers your care team may use:
- Moderate sedation is the most common approach. You stay drowsy and relaxed, can breathe on your own, and may respond to a tap on the shoulder or a verbal prompt, but you’re unlikely to remember much of the procedure.
- Deep sedation puts you further under. You won’t respond to voices and will only react to stronger stimulation. This is often administered by an anesthesia provider and is increasingly used at outpatient endoscopy centers.
- Minimal sedation keeps you awake but calmer. You can follow instructions and remain aware of your surroundings. This is less common for colonoscopy.
Your doctor will recommend a level based on your health, your anxiety level, and the complexity of the exam. In most cases, you’ll feel little to nothing during the procedure and won’t recall it afterward.
What Happens During the Exam
You’ll lie on your side on the exam table, usually with your knees drawn toward your chest. Once the sedation takes effect, the doctor inserts the colonoscope, a thin flexible tube about the width of a finger, into your rectum. The scope has a tiny camera at the tip that sends a live video feed to a monitor, letting the doctor examine the colon’s lining in real time.
To get a better view, the doctor pumps small amounts of air, carbon dioxide, or water through the tube to gently inflate the colon. This is what can cause a feeling of mild cramping or pressure, though most sedated patients don’t notice it. The scope is long enough to reach the far end of the colon, where it meets the small intestine. The doctor advances the scope to that point, then slowly withdraws it, carefully examining the tissue on the way out. This withdrawal phase is where most polyps are spotted.
The actual exam usually takes 30 to 60 minutes. With check-in, sedation, and recovery time, plan to be at the facility for two to three hours total.
Polyp Removal and Biopsies
If the doctor finds polyps or abnormal-looking tissue, they can remove or sample it on the spot through the same scope. You won’t feel this happening. The method depends on the size of the growth:
- Very small polyps (under 3 mm) can be grabbed and removed with tiny forceps passed through the scope’s channel.
- Small polyps (up to about 7 mm) are typically removed with a cold snare, a thin wire loop that cinches around the base of the polyp and slices it off without heat. This is fast, effective, and carries low risk of bleeding.
- Larger polyps (above 7 to 8 mm) are removed with a hot snare, which uses the same loop technique but adds an electrical current to cut and cauterize the tissue simultaneously.
Removed tissue is collected and sent to a pathology lab, where it’s examined under a microscope to determine whether it’s benign, precancerous, or cancerous.
Recovery and Going Home
After the scope is removed, you’ll be moved to a recovery area where you’ll rest for 30 to 60 minutes as the sedation wears off. You may feel bloated or gassy from the air used to inflate your colon. This passes quickly, and passing gas is encouraged.
You can eat your normal diet as soon as you feel up to it unless your doctor says otherwise. Avoid alcohol for at least eight hours after the procedure. For the rest of the day, skip strenuous exercise and heavy lifting. You’ll need someone to drive you home, and most people feel back to normal by the next morning.
Getting Your Results
Your doctor will usually share preliminary findings before you leave, including whether any polyps were found and removed. If tissue was sent to the pathology lab, those results typically take one to two weeks. The number, size, and type of polyps determine when your next colonoscopy should be scheduled.
If no polyps are found during a high-quality exam, most people at average risk can wait 10 years before the next screening. Small, low-risk polyps (called hyperplastic polyps) generally don’t move up your timeline unless they’re large or found in certain parts of the colon. Precancerous adenomas or more concerning findings like high-grade dysplasia will prompt earlier follow-up, sometimes in as little as one to three years.
Risks and Complications
Colonoscopy is considered safe, but it carries a small risk of serious complications. A systematic review of screening colonoscopies found that severe bleeding occurs in roughly 16 to 36 out of every 10,000 procedures, most often after a polyp is removed. Bowel perforation, a small tear in the colon wall, occurs in about 8 out of every 10,000 procedures. Both are uncommon but can require hospitalization or additional intervention.
After your colonoscopy, contact your doctor if you experience severe abdominal pain, fever, heavy rectal bleeding, or dizziness. Minor bloating and a small amount of blood after a polypectomy are normal and typically resolve within a day.