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Colonoscopy prep tips that actually help

Most people say the prep is the hardest part of a colonoscopy. It's also the part that matters most: if the colon isn't clean, small polyps can be missed and the exam may need to be repeated. These tips make it easier and more effective.

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A few days before

  • Follow your own instructions first. Preps differ, and the sheet from the team doing your procedure beats anything online.
  • Review your medicines with that team, especially blood thinners, diabetes medicines (including insulin), iron pills and GLP-1 medicines like Ozempic or Mounjaro (more on GLP-1s and your scope). Don't stop a prescribed medicine on your own.
  • Skip seeds, nuts, popcorn, corn and raw vegetables for a few days. They're slow to clear.
  • If you're often constipated, say so ahead of time. You may need a longer or stronger prep.

The day before

  • Switch to clear liquids when your instructions say: water, broth, apple or white grape juice, sports drinks, plain gelatin and popsicles.
  • Avoid anything red, blue or purple. It can look like blood during the exam.
  • Drink extra clear fluids through the day so you don't get dehydrated.

Making the prep go down easier

  • Split it if your instructions allow: half the evening before, half early the morning of. Split dosing cleans better than drinking it all at once.
  • Chill it, drink it through a straw placed toward the back of your tongue, and chase each glass with a clear drink you like.
  • Sucking on a lemon wedge or a clear hard candy between glasses helps with the taste.
  • Walk around between glasses to keep things moving.
  • Before you start, put a barrier cream like zinc oxide or petroleum jelly on the skin around your bottom, and keep soft wipes nearby.

How to tell it's working

By the end, what comes out should be clear or light yellow liquid, like urine. A few small specks are fine. If it's still brown or has solid pieces by the morning of your procedure, call the number on your instructions.

The day of

Finish your last dose by the time your instructions give, then nothing by mouth until after the procedure. Bring a driver. Sedation means no driving for the rest of the day.

A good prep is the best way to make sure your colonoscopy only has to happen once.

— Brian Frank, MD

Questions about colonoscopy? Call (813) 400-0543 or send a message.

Dr. Brian Frank, MD
Written by Brian Frank, MD
Board-certified gastroenterologist (ABIM). Published October 11, 2026.

This page is general information, not medical advice. For a medical emergency, call 911.