What to Expect During a Colonoscopy

There are two broad reasons your doctor may have ordered a colonoscopy.

Screening in people without symptoms. Screening for colorectal cancer is recommended starting at age 45 for people without health problems or risk factors that raise their chance of colorectal cancer (NIDDK, August 2023). The U.S. Preventive Services Task Force recommends screening adults aged 45 to 75, with the decision between ages 76 and 85 made on an individual basis (CDC, June 2026). For people who are not at increased risk, colonoscopy as a screening test is recommended every 10 years (CDC, June 2026). Intervals are shorter for some people — personal or family history, inflammatory bowel disease, and previous polyps all change the plan, and recommendations differ by guideline edition and by country.

Investigating symptoms. Doctors also use colonoscopy to find the cause of bleeding from the anus, changes in bowel movements such as diarrhea, abdominal pain, or unexplained weight loss (NIDDK, August 2023). None of those symptoms can be assumed to be minor without an evaluation.

Less invasive options that are sometimes used first. Other screening tests include virtual colonoscopy (CT colonography, a CT scan of the bowel), flexible sigmoidoscopy (a shorter scope exam of the lower colon), and stool tests (NIDDK, August 2023). One common stool test is the fecal immunochemical test, or FIT, which uses antibodies to detect blood in the stool and is done once a year (CDC, June 2026). The trade-off is important: if a stool test, flexible sigmoidoscopy, or CT colonography result is positive or abnormal, a colonoscopy is needed to complete the screening process (CDC, June 2026). Which test suits you is a conversation with your own clinician.

• When you book: ask for your written bowel prep instructions. Patients are given written bowel prep instructions before a colonoscopy (NIDDK, August 2023). Confirm every timing below with the ordering provider or the facility — prep protocols differ by physician, by center, and by your other conditions.
• 7 or more days before: tell the ordering provider about every medicine and supplement you take, including blood thinners, diabetes medicines, and iron. Ask specifically what to do with each one and on which day. Any change is physician-directed.
• 3 to 7 days before (follow your sheet): you may be told to avoid high-fiber foods such as nuts, seeds, corn, and raw vegetables (NIDDK, August 2023).
• The full day before (and sometimes longer): follow a clear-liquid diet as instructed (NIDDK, August 2023). Many centers also ask you to skip red or purple liquids — check your sheet.
• Evening before and often again the morning of: drink the bowel prep laxative on the schedule you were given. These are commonly polyethylene glycol solutions (generic), sold under brand names such as GoLYTELY or MiraLAX, among others. The product, amount, and timing are physician-directed — use only what your prescriber specified.
• A few hours before arrival: most centers stop all intake, including water, at a set hour. Get that exact hour in writing from your facility rather than guessing.
• Yes/no, before the day: have you arranged a ride home? You must, because sedatives or anesthesia need time to wear off before driving (NIDDK, August 2023). Many centers will cancel without a named adult escort.
• Before the day: ask your provider's billing office and your insurer what this will cost you. Do not assume coverage based on anything you read online.
• The morning of: arrive at the time on your instruction sheet, bring a photo ID, your medicine list, and your escort's phone number.

1. Check-in and gown. You register, change into a gown, and a nurse reviews your medicines, allergies, and how the prep went.
2. IV placement. An IV needle is placed in a vein in your arm or hand to give sedatives, anesthesia, or pain medicine so you will not be aware or feel pain during the procedure (NIDDK, August 2023).
3. Sedation choice, agreed in advance. You can have general anesthesia (a controlled loss of consciousness) or conscious/moderate sedation (a depression of awareness), selected with a healthcare provider before the day (Cleveland Clinic). Ask which one is planned for you and who will be administering it.
4. Positioning. You lie on your side on the exam table, usually with knees drawn up. Monitors track your heart rate, blood pressure, and oxygen throughout.
5. The exam. The doctor passes the flexible tube with a camera through the rectum and along the colon, using air or carbon dioxide to open the bowel so the lining can be seen. Expect a sense of pressure or fullness afterward; under sedation, most people are not aware of the exam.
6. Polyp removal or biopsy, if needed. The doctor may remove polyps and send them to a lab for testing, and you will not feel the polyp removal (NIDDK, August 2023).
7. Completion. The scope is withdrawn and you are moved to recovery. A colonoscopy usually takes less than one hour (NIDDK, August 2023).

Routine and expected

• You stay at the hospital or outpatient center for about 30 to 60 minutes after the procedure while sedatives or anesthesia wear off (NIDDK, August 2023).
• Bloating, gas, and cramping as the air leaves your bowel, usually easing over the first few hours.
• Grogginess, poor memory of the recovery room, and unsteadiness for the rest of the day. No driving, no work decisions, and no alcohol that day.
• Light bleeding from the anus is normal if the doctor removed polyps or performed a biopsy (NIDDK, August 2023).
• You should expect a full recovery and a return to your normal diet by the day after the colonoscopy (NIDDK, August 2023). If polyps were removed, your team may give you specific diet or activity instructions for a short period — follow theirs over any general advice.
• Results: the doctor usually tells you what was seen the same day; lab results on any polyp or biopsy take longer. Ask before you leave how and when you will get them, and who to call if you have not heard.

Not expected after a colonoscopy

• Severe or worsening abdominal pain rather than passing gas cramps.
• Fever.
• Bleeding that soaks through, keeps going, or starts up days later — delayed bleeding can occur up to 2 weeks after the procedure and may require treatment with a second colonoscopy (NIDDK, August 2023).
• Repeated vomiting, dizziness, or weakness.

Confirm your specific aftercare instructions with your own care team, since they vary by facility and by what was done during your exam.

Routine side effects

• Gas, bloating, and mild cramping for several hours.
• A small amount of blood with the first bowel movements if polyps were removed or a biopsy taken (NIDDK, August 2023).
• Drowsiness and a sore throat or sore IV site, mainly on the day of the procedure.

Less common complications

Serious complications include perforation (a tear in the colon wall), bleeding, and reactions to sedation. According to NIDDK, citing a systematic review prepared for the U.S. Preventive Services Task Force and published in JAMA, a study of screening colonoscopies found perforation in about 3 out of every 10,000 procedures and bleeding in about 15 out of every 10,000 procedures. Your own risk depends on your age, your other conditions, and whether polyps were removed — ask your gastroenterologist what applies to you.

Call your doctor's office promptly

• Bloody bowel movements that do not get better, or fever (NIDDK, August 2023).
• Bleeding from the anus that returns in the two weeks after the procedure.
• Inability to pass gas or stool, or a belly that keeps swelling.

Call 911 or go to the emergency room

• Severe abdominal pain — this is the red-flag symptom that distinguishes a complication from the routine gas cramps most people feel. Severe abdominal pain, fever, bloody bowel movements that do not get better, bleeding from the anus that does not stop, dizziness, or weakness all mean you should seek medical care right away (NIDDK, August 2023).
• Fainting, chest pain, or trouble breathing.

If you are unsure which category you are in, call the number on your discharge paperwork — after-hours lines exist for exactly this.