Preparing for your Colonoscopy

A colonoscopy is a procedure to allow your doctor to examine the inside of your rectum and colon. This will allow the doctor to look for the potential cause of any symptom that you are currently having (bleeding, diarrhea, pain) or to identify possible signs of cancer. During the procedure, a long, thin tube with a light and camera will be inserted into your rectum to look at the inside of your colon. Therefore, it is very important that your colon be free of stool to allow a clear view.

What do I need to do to prepare for my colonoscopy?

About 20-25% of people having colonoscopies are found to have improper preparation which can lead to a repeat colonoscopy or missed diagnosis. Therefore, it is important to follow all your preparation instructions carefully, especially those for medications to clean out your colon and diet restrictions the day(s) before your colonoscopy.

Tell your doctor about all medications that you routinely take and ask if you should take them on the day of the procedure.

You also will need to have someone to drive you home from the procedure as you will need to have a sedative for the colonoscopy. Due to the sedative medication, you will also need to stay home the rest of the procedure day and not make any important decisions.

What medications do I need to take to clean out my bowels?

Medications used to clean out your colon are available as liquid or tablets; all must be taken along with an additional prescribed amount of liquid. Your doctor will decide on the best medication for you to take based on your health, medications that you take, your preferences for tablets or liquid, and any dietary considerations. Many doctors may recommend a “split-dose” regimen with the first round of medication taken the day/night before the procedure and the second round of medication taken about 4-6 hours prior to the procedure.

It is important to read the instructions carefully and take the medication at the proper time and along with ALL the recommended amount of liquid. The medication will cause significant diarrhea, so you will need to have close access to a toilet beginning shortly after you take the medication.

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Do I need to change my diet?

Yes, to help you prepare for your colonoscopy, you will need to follow a clear liquid diet, usually for about one day before the procedure. You will also need to stop eating and drinking the night before the exam. Additionally, you may need to avoid certain foods that have a lot of fiber (e.g., whole grains, raw vegetables, beans, and nuts and seeds) several days before the procedure. Ask your doctor to provide specific times for you to change your diet and to start and stop taking liquids by mouth.

Clear liquids do not contain pulp, solids, or cream. Your doctor may also recommend avoiding red- or purple-colored drinks or gelatin. In most cases, you may drink or eat the following:

• fat-free bouillon or broth
• gelatin in flavors such as lemon, lime, or orange
• plain coffee or tea, without cream or milk
• sports drinks in flavors such as lemon, lime, or orange
• fruit juice with no pulp, such as apple or white grape—avoid orange juice, pineapple juice, and other cloudy juices
• water

What is virtual colonoscopy?

A virtual colonoscopy is a type of procedure that uses x-rays and computer technology to create images of the inside of your rectum and colon. This may allow the doctor to see any abnormalities such as ulcers, polyps, or potentially cancerous areas in your colon. Although, you will not need to have sedation for this procedure, you will need to clean out your bowel and follow a clear liquid diet before the procedure. You will also need to drink a liquid (contrast media) before the procedure that allows the doctor to see your rectum and colon on the x-ray. If any abnormalities are found, you may then need to have a regular colonoscopy to further evaluate the findings.

Summary

The most important part of a successful colonoscopy procedure is the preparation to empty the bowel. Be sure to take all the bowel cleansing medication and liquid that your doctor prescribes and follow any dietary instructions carefully. Ask your doctor or pharmacist if you have any questions about taking your medication.

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AHFS® Patient Medication Information is used with permission. ©2025, the American Society of Health-System Pharmacists, Inc. (ASHP). The ASHP Data is a part of the AHFS Drug Information®️; ASHP is not responsible for the accuracy of transpositions from the original context.