How Do I Know When Colonoscopy Prep Is Complete?

Colonoscopy prep isn't fun for several reasons, the main one being how much you will poop. You may have diarrhea for 12 to 16 hours after beginning the process of getting your bowels ready for this procedure.

How long the colonoscopy prep process will take altogether varies, but passing clear or yellowish fluid that is free from fecal matter is an indication that your bowel prep is complete.

The time it takes to get to this point largely depends on your general gastrointestinal health and how closely you followed your bowel prep diet.

This article discusses bowel prep before a colonoscopy and how you can tell when it's over and done with.

successful colonoscopy bowel prep

Verywell / Jessica Olah

What Should Poop Look Like During Colonoscopy Prep?

The effects of bowel prep medication can begin as soon as 30 minutes to an hour after your first dose, and can last up to 16 hours. Most people do not continue to experience diarrhea after they've gone to bed on the night before the test.

When your bowel movements contain only brown liquids, this means you are almost finished with your bowel prep.

Your stools should eventually end up as a clear or yellowish liquid.

Two things to keep in mind:

  • If there is any cloudiness to your liquid stool, your bowel prep is not complete.
  • If you can see the bottom of the toilet after a bowel movement, this means your bowel prep has been effective and the procedure can go forward.

Why You Need to Finish the Entire Prep Process

Your stools may look clear before you complete your entire prep, but it's important to finish all of the prep steps anyway. You could still have stool higher in your colon that will come out later.

Your gastroenterologist needs your colon to be clear of all stool in order to visualize abnormal tissue that would otherwise be hidden by poop. This typically requires more than two or three bowel movements.

Completing all steps of your prep offers you the best chance of having a clear colon for your colonoscopy (and not having to repeat the test).

According to research published in the journal Gastroenterology, up to 25% of colonoscopies are canceled due to an unsuccessful bowel prep.

Tips for a Successful Colonoscopy Prep

There are a few things you can do before your bowel prep begins to ensure that it is complete in time for your procedure. Aside from following your healthcare provider's instructions to the letter, you need to stay hydrated and choose the foods you eat wisely.

What to Eat in the Days Leading Up to the Procedure

In the few days prior to your bowel prep, stick to the diet recommended by your gastroenterologist. Eat smaller portions and drink plenty of fluids.

Good food choices include:

  • Soups
  • Smoothies
  • Digestive tea like chamomile or peppermint
  • Lighter-colored foods
  • Pasta and rice
  • Steamed vegetables
  • Eggs
  • Chicken

Avoid eating:

  • Nuts and seeds, including bread and other products that contain them
  • Popcorn
  • Hard-to-digest foods like corn
  • Raw vegetables
  • Red meat
  • Fried foods
  • Anything containing purple, orange, or red dye

Your Diet the Day Before the Procedure

Your healthcare provider will advise you to consume a clear liquid diet during the day before your colonoscopy. Choose liquids such as:

  • White grape juice
  • Chicken broth
  • 7-Up or Sprite

Staying Hydrated

Staying hydrated is crucial. Your body needs enough water to function properly. Many of the negative events related to a colonoscopy occur because of dehydration.

Dehydration can easily happen with bowel prep products containing sodium phosphate.

To combat this, drink a lot, but only clear fluids. In particular, make sure to avoid anything containing purple, orange, or red dye. These dyes can look like blood and may interfere with the results of your colonoscopy.

Stomaching Bowel Prep Medication

To avoid nausea and vomiting when taking your bowel prep medication, chill it first and drink it through a straw. Throwing up the medication may result in an incomplete prep.

What to Do if You're Still Passing Stool

If come the morning of your colonoscopy you haven't finished your prep or your bowel movements aren't reduced to clear liquids, contact your healthcare provider's office. They may want to reschedule your procedure or recommend additional steps to finish clearing your colon.

This may involve:

  • Drinking a bottle of liquid magnesium citrate (up to four hours before the procedure)
  • Drinking large amounts of clear fluids (up to two hours before the procedure)
  • Using an over-the-counter enema

If these strategies don't work, contact your healthcare provider again. You may need to reschedule the exam, since they won't be able to adequately visualize your colon if there is still stool present.

Deciding to cancel your procedure is not an easy decision for a healthcare provider to make, but it is necessary if your colon is not completely clean. Even if you were to go ahead with the exam, you may get inadequate results.

Waiting to share information about your bowel prep and bowel movements with your provider is problematic, as it may mean they only discover that stool is still present once you are already sedated and the procedure has begun.


Before you get a colonoscopy, it's important that you follow the bowel prep directions given to you so that you know when the prep is done. Your stools should be clear, yellowish liquid near the end of the prep.

But don't stop then: Make sure to complete all the steps in the directions provided to you. Closely following these instructions will help ensure the colonoscopy is effective.

Frequently Asked Questions

  • Will a colonoscopy prep keep you up all night?

    You make wake up once or twice to go to the bathroom, but it shouldn't keep you up all night. However, some people are required to wake in the middle of the night to take a second dose of laxatives at least four to six hours before their procedure.

  • How long does it take a colonoscopy prep to clear bowels completely?

    It can take 12 to 16 hours for the bowels to completely clear. Eating a low-residue, soft diet for a day or more before starting the prep can help make it easier and faster.

  • Do you need an enema before a colonoscopy?

    Your provider may instruct you to use an enema the morning of your colonoscopy if the laxatives did not completely empty your bowels. If you need to do this, do so at least two hours before your scheduled arrival time.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Johnson DA, Barkun AN, Cohen LB, et al. Optimizing adequacy of bowel cleansing for colonoscopy: recommendations from the US multi-society task force on colorectal cancer. Gastroenterology. 2014;147(4):903-24. doi:10.1053/j.gastro.2014.07.002

  2. American Society for Gastrointestinal Endoscopy. Understanding bowel preparation.

By Julie Wilkinson, BSN, RN
Julie Wilkinson is a registered nurse and book author who has worked in both palliative care and critical care.