Side Effects of Colonoscopy Prep

A colonoscopy is a procedure that enables a gastroenterologist to examine the colon for tumors, ulcers, inflammation and sites of bleeding. Colonoscopy preps are medications prescribed to remove fecal matter from the colon to facilitate a clearer view of the lining of the colon. Colonoscopy preps are made of ingredients that can have side effects.

Gastrointestinal Effects

According to the National Institutes of Health, polyethylene glycol prep has a salty taste that may cause nausea and vomiting. A prep can also cause stomach cramps, dehydration and irritation of the rectum, according to the website A colonoscopy prep draws large amounts of fluids to the colon, leading to dehydration. Drinking water after taking the prep is advisable. Chilling the prep can also make it more tolerable. Patients who fail to have a bowel movement within two hours of taking the prep should seek medical help.

Kidney Problems

Colonoscopy preps containing sodium phosphates may cause serious kidney problems, according to Some patients may develop permanent kidney damage and require longtime dialysis. Permanent damage, however, is more likely in patients who already have kidney and heart problems. Such patients should inform the doctor of their medical histories before taking colonoscopy preps. Symptoms of kidney damage include decreased urination, swelling of the legs and ankles, sudden weight gain, wheezing and shortness of breath.


Patients with a known allergy to sodium phosphates and other ingredients found in colonoscopy preps should avoid taking them. Symptoms of allergic reactions include difficulty breathing, wheezing, rash, hives, itching, chest tightness and swelling of the face and tongue.

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