What You Should Know About Bowel Preparation 

What is bowel preparation and why is it necessary?

It’s extremely important that your colon be thoroughly cleaned before your colonoscopy. This will let your doctor clearly see any abnormalities such as polyps during the exam. Polyps are small growths in your colon that could turn into cancer. 

Cleansing your colon is called bowel preparation or “prep.” It involves taking medication that causes diarrhea, emptying your colon. The medication is taken by mouth and comes in liquid or tablet form. You will also need to change your diet during the day or two before the colonoscopyas directed by your physician.

What bowel preparation steps are involved before the colonoscopy?

Your doctor will prescribe the type of bowel prep that’s best for you. You’ll receive specific instructions. In general, here’s what you can expect:

  • You’ll change your diet at least one day before your colonoscopy. Usually, you’ll be limited to clear broth, tea, gelatin desserts, ginger ale, sherbet, and clear fruit juices like apple juice.
  • You’ll need to avoid red or purple gelatin desserts and liquids. 
  • Avoid dehydration during the prep by drinking more fluids than usual. 
  • Your doctor will tell you exactly when to stop eating and drinking before your
  • colonoscopy.
  • Carefully follow all the steps your doctor prescribes. 

Why is bowel prep important?

Your bowel must be clean so your doctor can thoroughly examine your colon. Many patients feel the bowel prep is the most difficult part of a colonoscopy, but you should try your best to fully complete the prep.

What are the types of bowel prep?

Several types of bowel prep medications are available, and the two medications used most often in bowel prep are described below. Your physician may recommend one of these or other available preps. 

Carefully follow your doctor’s instructions about the exact dose and timing of your prep. Some types of prep may be covered by your medical insurance. You’ll want to find out if you have any out-of-pocket costs.

Polyethylene glycol electrolyte solutions may come as a powder to be mixed with water before use. They’re available only by prescription and are taken by mouth. Although given in a greater volume than other products used in bowel prep, they’re often preferred for patients with kidney, heart and liver conditions. 

Sodium phosphate comes in tablet form to be taken by mouth and requires a prescription. In rare cases, sodium phosphate can cause kidney failure. Doctors consider this when deciding if sodium phosphate is appropriate for a given patient.

Note from Bob: Are the 2 types of prescription prep the only types of prep affered or should be supplemented with other preps?

What determines the type of prep I get?

Your medical condition is the most important factor. Tell your doctor if you’re pregnant, breast feeding or have a history of bowel obstruction. Also tell them if you have high blood pressure, heart, kidney or liver disease, or if you’ve had any of these diseases in the past. 

Mention any medication allergies you have to your doctor. If you’ve had difficulty with a bowel prep in the past, mention this too. Other factors in choosing the type of prep are the time of your colonoscopy appointment, your individual preferences such as taste and amount of medication, and out-of-pocket costs.

What if I forget to take the medication when I should, or remember too late to finish the prep?

Call your doctor and ask what to do if you’re unable to complete the bowel prep as advised.

What are the common side effects?

The type and severity of side effects differ among patients and vary with the product used. Some patients have nausea, vomiting, swelling in the abdomen or abdominal pain. A prep can cause kidney failure, heart failure or seizures, but this is rare. Your doctor will explain the possible side effects of the prep selected for you.


This information is intended only to provide general guidance. It does not provide definitive medical advice. It is very important that you consult your doctor about your specific condition.