Sometimes, the preparation solution a person drinks before a colonoscopy to clear the bowels does not work. However, there are ways to help the prep work more effectively.

A colonoscopy is a procedure in which a doctor inserts a thin, flexible tube with a camera and light on the end into a person’s colon. Colonoscopies allow doctors to look inside the colon for anything that could be abnormal.

As the doctor will need to see the lining of the colon, the bowels must be empty for the procedure to be successful. One of the main preparations for a colonoscopy involves drinking a special liquid or taking other oral laxatives that induce diarrhea and empty the bowels.

On some occasions, the prep may not work, and the bowels may not be empty by the time a person is due to undergo their procedure. As the doctor could miss important details by performing the colonoscopy without the bowel being empty, the procedure may need repeating or rescheduling.

In this article, we discuss what to do if the colonoscopy prep is not working. We also provide tips on how to drink all the prep and explain the other steps a person can take before a colonoscopy.

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The body’s response to the colonoscopy prep drink can vary among individuals. Most of the time, people begin to have bowel movements about 3 hours after drinking the solution, so if a person has not experienced bowel movements by this time, the prep may not be working.

However, a person should continue to consume the prep and drink plenty of clear liquids even if they are not noticing any effects.

People may sometimes need to take additional laxative products, but they should always speak with a doctor before doing so. If a person is experiencing severe constipation, they may require an enema.

It may be challenging to drink all of the colonoscopy prep, especially if a person does not like the taste. However, people can make the prep more drinkable by:

  • Splitting the prep: Rather than drinking the colonoscopy prep the evening before the colonoscopy, people can split it between the night before and the morning of the procedure.
  • Using a straw: Drinking the mixture with a straw can help it bypass the taste buds, so people are less likely to taste it.
  • Drinking the prep in sips: Instead of drinking the entire dose of prep in one or two sittings, people may find it easier to take sips and drink other clear liquids in between.
  • Chilling it: Anecdotal evidence suggests that prep drinks taste worse when warm, so it may help to refrigerate the prep or drink it over ice.

It is important to discuss these options with a doctor before trying them to make sure that they do not affect the specific prep that the person is taking.

A person needs to take additional steps before a colonoscopy to give the prep drink the best chance of emptying the bowels before the procedure. These include:

Making dietary changes

Doctors will likely recommend that people switch to a low fiber diet a few days ahead of the colonoscopy.

People on a low fiber diet tend to avoid:

  • foods made from whole wheat flour, graham flour, and bran
  • cornbread
  • granola
  • brown and wild rice
  • nuts and seeds
  • raw vegetables
  • raw and dried fruits
  • the skin of fruits and vegetables
  • fruit juice with pulp

The day before a colonoscopy, people will usually need to change to a fully liquid diet.

A fully liquid diet allows:

  • any water
  • clear fruit juices with no pulp, such as apple or white grape
  • gelatin, such as Jell-O
  • tea or coffee without milk or cream
  • clear sports drinks
  • clear, fat-free broth
  • popsicles

If a person is unsure whether they can consume a specific product, they should check with a doctor.

People must take particular care to avoid anything containing purple, blue, or red colorings, as these can resemble blood in the colon and may give misleading results.


People should stay close to a bathroom even if they believe that they may be constipated. The prep could take slightly longer than usual to work but then suddenly be effective.

Wearing loose and elasticated pants without buttons may save time in case of urgency.

Frequently having loose stools may cause a person to experience soreness around their anus, so liberally applying Vaseline or a similar product may help reduce the discomfort. People could also use flushable baby wipes or moistened toilet tissues instead of toilet paper to reduce irritation.

The doctor may have provided a leaflet with the prep drink that details what an individual should do if they have not had a bowel movement after consuming all of the colonoscopy prep drink. If not, a person should make their doctor aware of the issue.

It is important to speak with a doctor before trying anything else to help encourage bowel movements.

Constipation may occur after a colonoscopy. For this reason, people should avoid fatty or greasy foods for the first few days after the procedure.

Although people can return to the diet that they had before the procedure, some individuals may choose to eat more bland foods initially to prevent irritation as the bowels refill.

Having no bowel movement after colonoscopy prep is uncommon, but it can happen.

If someone does not have a bowel movement after consuming all of the prep drink and taking other preparatory actions, they should contact a doctor.