How to Know When Bowel Prep Is Complete

Bowel prep is something you must do to clean out your colon before getting a colonoscopy. A colonoscopy is a medical test that examines the colon (large intestine) and rectum. During the procedure, the healthcare provider uses a flexible camera called a scope to search for any potential problems like bleeding, polyps (small growths), or signs of cancer.

Although it's not a fun experience, completing a bowel preparation doesn't hurt. In other words, there's no reason to run for the hills when it's time to prepare for this all-important screening.

This article will discuss all the things you need to do to get ready for your colonoscopy, including how to know to when your bowel prep is done.

successful colonoscopy bowel prep

Verywell / Jessica Olah

Things to Do Before You Begin

Before you begin your bowel prep, talk to your healthcare provider if you have any heart, kidney, or liver problems. With some medical conditions, a healthcare provider will need to change the type of bowel prep you use. Some treatments are safer than others when it comes to certain medical conditions.

There are many options, so don't worry that you won't be able to have the test done. It's important to make sure the healthcare provider performing your colonoscopy is familiar with your medical history for other reasons too. Some medications, such as blood thinners, can increase the risk of complications from bowel prep.

Review Your Instructions

First of all, make sure you stay close to home. That's because you'll be using the toilet many, many times before the process is through.

Your gastroenterologist (a healthcare provider who treats conditions related to the digestive system) needs to get every bit of stool (poop) cleaned out of your colon. This will probably require more than two or three bowel movements. It will make it possible for your healthcare provider to see abnormal tissues that might be hidden by what's inside your bowel.

All gastroenterologists follow the cleansing guidelines approved by the American Gastroenterological Association, American College of Gastroenterology, and American Society for Gastrointestinal Endoscopy.

But each healthcare provider may order the bowel prep a little differently. The instructions can even vary based on what time you'll be getting the test. What a healthcare provider tells your friend to do for a bowel prep might not be the same instructions you receive. This is normal.

Before your healthcare provider gives you directions on how to complete your bowel prep, they will consider:

  • Your health
  • What you may or may not be able to tolerate
  • What has worked best in the past

There are some types of preps that you shouldn't do if you have certain medical conditions. A healthcare provider may recommend one bowel prep for you and another for someone else.

Getting Started

Most bowel preparations begin with a liquid you drink or pills you swallow. You might start to see effects as soon as 30 minutes to an hour after your first glass of solution or your first pill. Your first bowel movements will most likely be a combination of firm, semi-firm, or loose brown stools. 

Continue to drink plenty of clear liquids and keep yourself hydrated. Avoid commercial drinks with purple or red dye. These dyes can interfere with your colonoscopy results.

Staying Hydrated

The importance of staying hydrated can't be stated enough. When you are hydrated, your body has enough water inside of it to work properly. Many of the negative events related to colonoscopy are because a person was dehydrated during the procedure. Dehydration can easily happen with bowel prep products containing sodium phosphate.

You might notice some uncomfortable, but not painful, side effects of the bowel prep. Stomach cramping and gas are completely normal. Laying a clean, damp cloth on your stomach can help with any discomfort. A small bit of activity—such as a walk around the house—may also help relieve uncomfortable side effects.

Following each step of your healthcare provider's bowel prep instructions is very important. Sometimes it may seem like you're just repeating steps, such as using an enema after having several bowel movements. But there's a reason for the entire process.

Finishing the Bowel Prep

When your bowel movements contain only brown liquids, you are almost finished with your bowel prep. The color of your stools eventually ends up a yellowish clear liquid. If there is any cloudiness to your liquid stool, your bowel prep is not complete.

At some point, you may find that your stools have become clear, liquid, and yellowish before completing your entire prep. It's important to finish the prep anyway. Sometimes, stool that is higher in your colon hasn't left your body yet. Completing all steps of your prep offers you the best chance of having a clear bowel for your colonoscopy (and not having to repeat the test).

Just because your stools are clear, liquid, and yellowish doesn't mean your bowel prep is over. It's important to follow all of the bowel prep steps. Following each step exactly makes sure you have a clear bowel and you're ready for your colonoscopy.

Why Bowel Prep Matters

According to research published in the journal Gastroenterology, up to 25% of colonoscopies are canceled due to an unsuccessful bowel prep. Deciding to cancel your procedure is not an easy decision for a healthcare provider to make. This is because you are most likely sedated and the practitioner has already started the procedure. The healthcare provider can only perform the colonoscopy if the colon is completely clean.

If you didn't finish your prep or your bowel movements aren't reduced to clear liquids, contact the healthcare provider so you can reschedule your procedure.

There's really no way to know for sure whether your bowel prep is complete before you have a colonoscopy. In fact, it's not unusual for people to have an incomplete prep that requires the healthcare provider to reschedule the exam.

Sometimes you may have the exam but receive inadequate results. This often happens when people skip one of the steps of the prep because they believe they are done. It can also happen because they don't think all of the steps are necessary.

The best way to make sure your bowel prep is complete is by performing each step of the bowel prep just as your healthcare provider recommends.


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. Closely following these instructions will help ensure the colonoscopy is effective.

A Word From Verywell

Preparing for a colonoscopy isn't exactly fun, but it's an important exam that can help you live a long, healthy life. By following your healthcare provider's bowel prep directions, you will prepare for the colonoscopy effectively so you can put it behind you and move on with your life.

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4 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.
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  2. Harvard Health. Preparing for a colonoscopy.

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

  4. 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