Colonoscopy Prep: What You Need to Know
July 09, 2024
Updated on November 11, 2025
Getting a colonoscopy might not be at the top of your bucket list, but it’s an important screening tool to catch colorectal cancer, the third most common cancer in the U.S. Most people should start getting colonoscopies at age 45. If you have colorectal cancer symptoms or risk factors, such as a family history of the disease, you should start even earlier.
Many people dread preparing for their colonoscopy, says Thomas Lake, M.D., colon and rectal surgeon at Jersey Shore University Medical Center and Ocean University Medical Center. But there are ways to make yourself more comfortable and smooth the process.
What Is Colonoscopy Prep?
A few days before your screening, you must prepare your body for your colonoscopy. You’ll change your diet and take laxatives, a medication that makes your stool more watery and helps your body push stool out.
Why You Need Colonoscopy Prep
Bowel prep can be unpleasant, but it’s key to a successful colonoscopy. You need to empty your bowel, so your doctor can see inside your colon and rectum.
“The better the prep, the better the exam,” says Dr. Lake. “If someone doesn’t prep well, we could miss potentially dangerous findings.”
If you don’t prepare well enough, you may also need to reschedule your colonoscopy and face the process again. Follow your doctor’s instructions, and use the following tips for a smooth and successful prep.
1. Choose Your Prep
There are different laxatives you can take for colonoscopy prep. Most are liquid, though a pill option is also available. All require you to drink a lot of liquid—between two and four liters.
“Whether it's liquid medication or pills combined with drinking a lot of water, you're drinking plenty of fluid either way,” Dr. Lake says.
Some laxatives are not safe if you have kidney or heart conditions. Your doctor will help you choose the best prep option for you.
2. Plan for Success
Start planning your prep a few days before your colonoscopy to make the experience as easy as possible. Make sure you have everything you need, including:
- The prep kit
- Flavorings, sweeteners or drinks your doctor has OK’d to mix with the laxative
- Clear liquids, such as clear broth, juices and popsicles
- Soft toilet paper or soothing wet wipes
- Vaseline or diaper cream you can apply to clean, dry skin between bowel movements
- Something to read or watch while you’re in the bathroom, and a charger if needed
- Someone to drive you home from your colonoscopy
3. What to Eat – and Not to Eat – During Colonoscopy Prep
A few days before the procedure, stop eating high-fiber, fried and heavy foods, such as:
- Red meat
- Raw vegetables
- Nuts and seeds
- Apples
- Corn
Eat small meals of low-fiber, low-fat foods, such as:
- Rice
- Eggs
- Steamed vegetables
- Brothy soups
- Smoothies
Stop eating solid food the day before your colonoscopy, and switch to a clear liquid-only diet. Don’t eat or drink anything bright red, orange or purple. These colors can look like blood on your screening.
4. Start Your Medication the Night Before Your Colonoscopy
Follow your doctor’s instructions to start your prep on time. You need to give your body enough time for the laxative to work. If you forget or start too late, you may have to reschedule.
5. Drink Your Laxative Cold, Flavored and Slowly
Some people struggle to drink their laxative. But there are some ways to make finishing the drink easier.
- Drink it cold, and try using a straw.
- Flavor it. The taste of laxatives varies. Some have a slight lemon flavor while others have no flavor. Most can be sweetened or mixed with other fluids, like sports drinks, to improve the taste.
- Break it up. Your prep kit’s instructions will tell you how long you have to finish the drink. For example, if you have one hour, try dividing the drink into four servings, and drink one every 15 minutes.
- Chase it. Sip a tasty clear liquid after each gulp, or suck on a candy or lemon wedge.
If you get queasy easily, tell your doctor. They can prescribe anti-nausea medication, Dr. Lake says. If you still have nausea, he recommends taking an hour off from drinking the prep. “We don’t want anyone to drink the prep too fast and then vomit,” he says.
Call your doctor if you’re vomiting or the laxative is not working. They can troubleshoot with you and may prescribe more medication.
“I like to prep early in the day, so we have time to come up with a plan B if they have any trouble,” says Dr. Lake.
6. Get Settled In or Near the Bathroom
Once the laxative starts working—in about one to six hours—expect diarrhea. Stay close to a bathroom. You might have cramps, gas and bloating. Continue drinking clear liquids, so you stay hydrated. Drinks with electrolytes are a good choice. When you finish your prep, your stools should be a clear or slightly greenish liquid. If they aren’t, tell your doctor.
The Day of Your Colonoscopy
Stop drinking all liquids four hours before your procedure. Make sure to finish all of your laxative drink doses, even if your stools are already clear.
After a successful prep, the hard part is over. Pat yourself on the back for making your health a priority and getting screened.
Next Steps & Resources:
- Meet our source: Thomas Lake, M.D.
- Make an appointment with a primary care provider near you to see if you’re due for cancer screening, or call 800-822-8905.
- Learn more about gastroenterology at Hackensack Meridian Health.
The material provided through HealthU is intended to be used as general information only and should not replace the advice of your physician. Always consult your physician for individual care.
