A colonoscopy preparation is needed before the procedure. This is to clear the large intestine (colon) of stool so a healthcare provider can get a good view of the organ's lining. Various preparation methods are used.
Several different types of laxatives can clear the bowel of stool. It will also be important to eat a low-fiber diet in the days leading up to a colonoscopy, a clear liquid diet the day before, and stop all liquids several hours before the appointment.
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Bowel Prep Before Colonoscopy
The goal of the bowel prep is to clean out the large intestine of stool. Bowel preps usually consist of one or more types of laxatives and also drinking electrolyte drinks to prevent dehydration. Electrolytes are charged molecules such as sodium, potassium, and calcium that are critical for cell function and fluid balance.
When the intestine is as empty as it can be, the lining is easier to see. This allows healthcare providers to find polyps (growths), inflammation, diverticula (outpouchings), or anything else that could be a problem.
No matter which laxative type is used, the result will be watery diarrhea. It's important to stay near a bathroom and monitor these bowel movements to ensure that the colon is cleaned out enough for the colonoscopy. A healthcare provider will give specific instructions.
Following is some general information about how some colonoscopy preparations are used.
High-Volume PEG
A combination solution of high-volume polyethylene glycol (PEG) and electrolytes is available under the following brand names:
- Colyte
- GaviLyte-C
- GaviLyte-G
- GoLYTELY
- NuLYTELY
- TriLyte
These preparations contain a powder that is mixed with 4 liters of water. There are several brands, and each contains different types of electrolytes along with the laxative.
To clear the colon for a colonoscopy, it's standard practice to start drinking the solution the afternoon before a test scheduled for the next morning or the evening before a test scheduled for the next afternoon. The usual recommendation is to drink 8 ounces of the liquid approximately every 10 to 15 minutes until it is all gone or the stools are clear or light yellow.
Low-Volume PEG
Low-volume prescription PEG and electrolytes are available under the brand names MoviPrep and Plenvu. These preps contain PEG and ascorbic acid as laxatives, plus other ingredients. They are taken in two doses of 16 ounces for a total of 32 ounces, which is much less liquid than the high-volume prescription preparations.
They are used as a split prep, meaning one dose is taken the day before the procedure and another several hours before the procedure (which could sometimes be the middle of the night, depending on timing). They usually have flavorings to help them be easier to drink.
OTC PEG
Polyethylene glycol is available over the counter (OTC) under the brand name MiraLax and as a generic in many drugstores.
Your healthcare provider may recommend mixing 238 grams of the polyethylene glycol powder into 64 ounces of a clear liquid. Then, it should be divided into two 32-ounce portions. Some healthcare providers recommend mixing it with an electrolyte replacement drink, such as Gatorade or SmartWater.
You may be asked to drink the first 32 ounces the afternoon before your colonoscopy by drinking 8 ounces every 15 minutes. Bowel movements may start about an hour after drinking the first 8 ounces.
You must drink the second half of the polyethylene glycol preparation either later that same night for a morning colonoscopy or the next morning for an afternoon colonoscopy. A healthcare provider may also give instructions to take a stool softener such as Dulcolax (bisacodyl) in two doses along with the polyethylene glycol.
OsmoPrep
OsmoPrep and Visicol Tablets (sodium phosphate monobasic monohydrate, sodium phosphate dibasic anhydrous) are available by prescription. This prep involves taking tablets and about 64 ounces of fluids to clear the colon of stool.
This type of prep might not be suitable for people who live with heart failure or kidney issues or who are at risk for an electrolyte imbalance.
Clenpiq
Clenpiq (sodium picosulfate) comes as two 6-ounce doses of premixed liquid. It's a split dose prep, meaning that one dose is taken the day before, and another two hours before the procedure. It's also recommended that the person drink 40 ounces of liquid with the first dose and 32 ounces of liquid with the second dose.
Clenpiq might not be for use in people who live with heart failure or kidney issues or who are at risk for an electrolyte imbalance.
Sutab
Sutab (sodium sulfate, magnesium sulfate, potassium chloride) is a prescription colonoscopy prep consisting of 24 tablets. They are taken in two doses of 12, one dose the night before and the second dose five to eight hours before the procedure. It's also important to drink 16 ounces of liquid within 20 minutes of taking each dose, and another 32 ounces of liquid over the next few hours.
Sutab might not be for use in people who live with heart failure or kidney issues or who are at risk for an electrolyte imbalance.
Suprep
Suprep (sodium sulfate, potassium sulfate, magnesium sulfate) comes as two 6-ounce bottles of liquid. The first bottle is mixed with 10 ounces of water and taken the night before the colonoscopy. The second bottle is prepared the same and taken 10 to 12 hours after the first dose. After each dose, it's important to drink 32 ounces of water.
What's the Easiest Colonoscopy Prep?
With so many different types of preparation available, people can choose the one they think will be best for them. Some preps require measuring and mixing, while others come ready to go. Some preps involve taking tablets, while others involve drinking various amounts of liquids.
Working with healthcare providers to discuss the pros and cons of colonoscopy preps is important. Providers may prefer to prescribe a certain type because it works reliably well for their patients.
However, if the prep doesn't seem like it would be the best option for you, ask if there is another prep that you can use. The best prep for you is the one that you can obtain (some preps may be costly) and that you can finish.
Prep Process Hour by Hour
The prep for a colonoscopy may begin several days or weeks before the procedure. Instructions from the healthcare provider may include a list of any foods to avoid or medications to discontinue or adust in the days before the test. These may include iron supplements, drugs that affect gut motility, such as Ozempic (semaglutide), diabetes medications, and blood thinners.
Day before the test: Cleaning out the bowel of stool usually begins the day before the colonoscopy. Some people may be told that they can eat a small breakfast of low-residue foods. After that, it will be important only to consume clear liquids that do not contain red, orange, or purple food coloring. They may drink black coffee, tea (without milk), chicken broth, ginger ale, apple juice, and sports drinks and eat gelatin.
Evening before the test: In the evening of the day before the test, usually around 4 p.m. or 5 p.m., it will be necessary to start the prep, whether taking laxative tablets or drinking a laxative preparation. Bowel movements may start within an hour of taking the prep and will continue for several hours.
A split prep is now used fairly commonly. This means that part of the prep is taken in the evening, and the second part is taken a few hours before the scheduled time of the procedure.
Morning of the test: If a split prep is used, the second part should be started at the time recommended by the healthcare provider. There will be more bathroom trips, and bowel movements should begin to appear light yellow or clear. This is a good indicator that the colon is clear of stool and the prep has been completed.
The instructions from the healthcare provider will give timing on when all clear liquids should be stopped. This usually is between two and four hours before the time of the test.
It may be possible to take certain medications with a sip of water. Check with your healthcare provider on any medications taken in the morning.
Arrive for the test: Once the colon is clear of stool, the colonoscopy can take place. The person will be checked into the hospital or endoscopy facility and prepped for the procedure.
After the test: Upon completion of the colonoscopy, most people will be able to have something to drink and a snack. If feeling well enough, they can eat a small meal within a few hours of the test.
Foods to Eat or Avoid
You will be given a short list of foods that should be avoided starting about one week before the colonoscopy. In general, a low-fiber diet is recommended in the days leading up to the test. Foods that are more difficult to digest should be avoided. This includes fresh fruits and vegetables, whole kernel corn, whole grains or seeds (including poppy or sesame seeds), and nuts.
Once on a clear-liquid diet, it is important not to eat any solid food. A clear liquid diet does include some things that are not liquid, such as popsicles, gelatin, hard candies, and gummies. Any questions about what is and isn't included in a liquid diet should be directed to a healthcare provider.
Having a variety of clear liquids on hand may help with becoming bored with drinking water and feeling too hungry.
Some of the types of clear liquids that people can have while prepping for a colonoscopy include:
- Black coffee (no milk or cream)
- Clear broth, bouillon, or consommé
- Clear fruit juice (lemonade, apple, white cranberry, and white grape)
- Flavored ices
- Gelatin (Jell-O, but no red, purple, or orange)
- Hard candy
- Lemon/lime soda (7UP, Sprite), ginger ale, and seltzer
- Sports drinks (Gatorade and Powerade, but no red, purple, or orange)
- Tea (no milk or cream)
Avoiding Dehydration
Part of the bowel prep for a colonoscopy is having watery diarrhea. This can result in losing more water than is being taken in through food and drink. It's important to keep drinking liquids to avoid becoming dehydrated.
Look for signs of dizziness, thirst, and fatigue and if you are urinating less frequently, which can indicate dehydration. Your healthcare provider will give instructions on how much clear liquids to drink while prepping. Call your healthcare provider with any questions or if you think you are becoming dehydrated.
Benefits of Prep
The purpose of a colonoscopy is to view the colon walls for abnormalities. It's important to have a good prep before having a colonoscopy. The colon needs to be as clear of stool as possible. When there is no stool in the colon, the walls on the inside can be better seen.
A colonoscopy looks for abnormal growths called polyps. These are the precursor to colon and rectal cancer. Any polyps found will be removed (called a polypectomy) whenever possible. Some polyps can be flat and more difficult to spot, making a good prep important.
Removing a polyp means that it can't turn cancerous. This prevents colon cancer.
Will You Need Another Colonoscopy?
A colonoscopy will need to be repeated if it can't be completed due to incomplete preparation. Stool in the colon can prevent a clear view of the colon, making it difficult for the provider to see any and all polyps.
For people who are at average risk for colorectal cancer, the interval for screenings may be every 10 years. If there is a finding, or there are polyps removed, there may be a need to have another colonoscopy sooner than 10 years (such as three or five years).
People who have a family or a personal history of colon and rectal cancer or who live with a digestive condition may need to have colonoscopies more frequently, even yearly.
End of Prep: Same Night or Next Day?
The prep ends when all of the preparation is taken. However, people may continue to need to use the bathroom until it is time for the test.
Follow your healthcare provider's prep instructions, including whether to do a split prep. If you have any questions on timing, discuss them before you start the prep.
Doing the prep in two parts—one the night before and one several hours before the appointment—works just as well as doing the prep all at once. It may even work better in ensuring that the prep is complete and that even smaller polyps can be found.
Summary
Many colonoscopy preps are available. A healthcare provider will give instructions on how to follow the prep. It's important to understand all the instructions before starting and to make any preferences known (such as taking pills over drinking liquids).
When the prep is completed, the colon should be clear of stool. This helps a healthcare provider see the colon's lining and any polyps or other abnormalities there.
