5 Things Gastroenterologists Wish You Wouldn't Do Before a Colonoscopy

Your gastroenterologist will tell you to avoid red liquids before a colonoscopy.
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If you're over 45, or are dealing with a gut health issue, you may be advised to get a colonoscopy.


Colonoscopies are important medical exams where doctors use a camera on a long tube (aka, a scope) to look at the inside of your colon. It can help find answers for things like internal bleeding, changes in bowel movements, pain in your belly or unexplained weight loss. Doctors also use them as a tool to diagnose certain cancers — like colorectal cancer, according to the National Institute of Diabetes and Digestive and Kidney Diseases.

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In order to prep for this procedure, you'll often be prescribed an oral laxative to empty your bowels. Beyond that, there's a few things to do (and ‌not‌ do) before you get a colonoscopy to help it go smoothly — like eating the right foods or avoiding certain drinks.

Here, learn what gastroenterologists wish people ‌wouldn't‌ do before a colonoscopy, and how to best prepare for the procedure.

5 Things Not to Do Before a Colonoscopy

Sarah Robbins, MD, gastroenterologist and founder of Well Sunday Health Corporation, shared five of the biggest mistakes she sees people make before a colonoscopy.


While these may not seem like a big deal, they can affect the results of your exam, and possibly interfere with your diagnosis.

1. Don't Eat Solid Foods Less Than 24 Hours Before the Procedure

Your doctor or outpatient facility where you'll get your colonoscopy should tell you to stop eating solid foods 24 hours before the procedure, Dr. Robbins says.


Fasting — along with drinking a prescribed laxative — is done to make sure your colon is completely empty and free of stool.

If you eat something (that's not clear liquid) too close to the exam, your doctor's view through the camera may be obstructed, Dr. Robbins adds.

2. Don't Continue Taking Certain Medications

Another common mistake people make is continuing to take medications that may actually interfere with a colonoscopy.


This is why it's important to tell your doctor about all medications you're taking, including over-the-counter meds, to see if they'll be a problem, Dr. Robbins says.


"For example, blood thinners may need to be stopped a few days before the procedure to prevent bleeding complications," she says. "You should also stop taking iron and fiber supplements five days before the procedure."


Other medications that have recently caused issues with colonoscopies are GLP-1 meds like Ozempic, Mounjaro and Wegovy — used to treat diabetes and obesity.

According to an October 2023 study in ‌The American Journal of Gastroenterology,‌ these medications slow down your digestion and reduce the effectiveness of bowel prep for colonoscopies. This means you may need even more bowel prep to avoid having to redo the colonoscopy.



Talk to your doctor before stopping any medications you're currently on. They can let you know which ones are safe to continue using during colonoscopy prep, and which ones aren't.

3. Don't Drink Red, Blue or Purple Liquids

According to Dr. Robbins, it's important to avoid drinking red, blue or purple liquids when you're on a clear liquid diet for colonoscopy prep.

These colors can stain your colon and be mistaken for blood during the colonoscopy, Dr. Robbins says. "They can also make it hard to properly see your colon tissue," she adds.


4. Don't Drink Alcohol

While certain liquors are technically clear liquid (which is allowed during colonoscopy prep), "alcohol can cause dehydration and may interact with some of the medications used during the colonoscopy," Dr Robbins says.

For this reason, it's best to avoid all alcohol the day of your colonoscopy, as well as the day before.

5. Don't Eat High-Fiber Foods

While they're typically great for your gut, high-fiber foods (like oats, bran, beans or broccoli) can interfere with the bowel cleansing process, Dr. Robbins says.


"It's recommended to start reducing your fiber intake a few days before you start the clear liquid diet; my recommendation is at least five to seven days before the test," she says.

Why It's Important to Follow Colonoscopy Prep Guidelines

“The primary goal of a colonoscopy is for your doctor to get a detailed look inside your colon,” Dr. Robbins says.

This means your colon needs to be as clear as possible. “A well-prepped bowel is like a sparkling clean window, offering the doctor an unobstructed view,” she adds.

Even the tiniest polyp or abnormality can be harmful to your health, so a clear bowel can help your doctor pick up on these details, and give you an accurate diagnosis.

“This accuracy is vital, especially when screening for conditions like colorectal cancer or inflammatory bowel disease,” Dr. Robbins says.

A properly prepped colon also reduces your risk of complications from the procedure, she adds. If your doctor can clearly see where to move the camera, there's a lower chance of accidental injury to your colon wall.

Lastly, any inconclusive exam results may require you to get the procedure done again, which can be inconvenient (plus, you'd have to do the prep all over again).

Tips for Successful Colonoscopy Prep

While every colonoscopy prep is slightly different depending on your doctor and individual health needs, here are a few general guidelines to help you best prepare:

1. Start Planning Five to Seven Days in Advance

If you start planning early, your procedure will be more accurate, safe and less stressful, Dr. Robbins says.

Give yourself five to seven days to ask your doctor about any medication adjustments to make, reduce fiber intake or buy any food or drinks you may need.

2. Take Medications Well Before (or After) Taking the Laxative

If your doctor gives the OK to keep taking prescription medications during your colonoscopy prep, "try to avoid taking them within two hours before or after taking the prescribed laxative," Dr. Robbins says.

Taking them too close together, or at the same time, could cause your prescription to be ineffective/not properly absorbed by your body, per the Mayo Clinic.

And talk to your doctor if you take medications that need to be taken at specific times of day — like diabetes medication, blood thinners or anti-thrombotic drugs (medicines that prevent blood clotting), for example. In this case, your doctor may need to adjust your dosage schedule.

3. Try Out This Five-Day Dietary Plan

To help you remember what to start (or stop doing) and when, Dr. Robbins recommends this general plan:


  • Five days before the procedure:‌ Stop taking fiber supplements and stop eating high-fiber foods.
  • Four days to one day before the procedure:‌ Start eating a low-fiber diet. This could include certain cooked vegetables, canned fruit, white bread, white pasta, rice, dairy products, meat, eggs, tofu or smooth nut butters. Avoid nuts, seeds, popcorn, raw fruits and vegetables, whole grains and other high-fiber foods, per Kaiser Permanente.
  • One day before the procedure:‌ Have a light breakfast (like plain toast, clear juice, tea or coffee without milk). Don't eat any solid food after breakfast. Drink clear fluids like tea, coffee, clear juices, sports drinks, clear broth and water. Avoid red, purple or blue fluids, milk products, alcohol or meal replacement drinks, per Kaiser Permanente.
  • Follow the colonoscopy prep provided by your doctor:‌ There are several different methods for cleansing your colon prior to a colonoscopy, including taking a prescribed laxative or using enemas. Try to follow the exact instructions of your doctor's preferred method.

Keep in mind that these dietary instructions are only a guide. Talk to your doctor about your specific needs, or if you're unsure of what to do.


Talk to your doctor if you deal with chronic constipation. You may need extra bowel prep to be ready for a colonoscopy.

4. Plan How You'll Get Home After the Exam

Not many people think about what happens after a colonoscopy, but because you've been sedated, you may need to come up with a plan on how to get home, Dr. Robbins says.

"I can't tell you how many times we've had to cancel a procedure because the patient had no safe way home," she adds. Sedation means you can't drive for at least eight hours, so ask a friend or family member to drive you to and from the procedure.

Dr. Robbins says it's also recommended to avoid traveling for two weeks after the procedure, in the rare case you get any complications.

The Bottom Line

While there are steps you have to take before getting a colonoscopy, there are also things you ‌shouldn't‌ do — to make sure your procedure is safe and effective.

Talk to your doctor if you're unsure about what foods, drinks or medications you can and can't have.




Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.

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