How do I prepare for a colonoscopy?
A clean bowel is what makes a colonoscopy accurate. Preparation has five stages: telling the clinic about your medicines about a week before, a low-fibre diet for one to three days, clear fluids and the bowel-cleansing drink the day before, fasting on the morning, and going home with a companion. Your written instructions always come first.
About a week before
Tell the clinic every medicine you take
Some medicines need to be paused or adjusted before a colonoscopy, so tell the clinic early about everything you take. This matters most for blood thinners, diabetes medicines, weekly injections for diabetes or weight loss, and iron tablets. Do not stop anything on your own; follow the written plan you are given.
- Blood thinners and antiplatelet medicines, such as warfarin, apixaban, rivaroxaban or clopidogrel
- Diabetes medicines and insulin, because you will be eating less
- Weekly GLP-1 injections such as semaglutide or tirzepatide, which slow stomach emptying
- Iron tablets, which darken the stool and make the bowel harder to see
- Any supplements, and whether you have had a colonoscopy before
1 to 3 days before
Switch to a low-fibre diet
Low-fibre food leaves less residue in the bowel, so the bowel preparation works better. Guidelines limit this to the day before for most people, while some clinics ask for up to three days. Follow the number of days in your own instructions.
Usually allowed
- White rice, porridge
- White bread, plain noodles
- Eggs, tofu
- Fish, skinless chicken
- Clear soups
- Water, clear apple juice
Usually avoided
- Fruit and vegetables
- Brown rice, oats, wholegrains
- Nuts, seeds, beans
- Red meat
- Milk, yoghurt, creamy soups
- Red, purple or dark drinks
More detail: what to eat and avoid before a colonoscopy.
The day before
Clear fluids and the bowel preparation
The day before, you move to clear fluids and take the bowel-cleansing drink at the times on your instruction sheet, often split between the evening and early morning. Expect frequent, watery stools. The prep has worked when what you pass is clear or pale yellow liquid.
- Stay near a toilet once you start the preparation
- Drink plenty of the allowed clear fluids so you do not become dehydrated
- Finish the whole preparation; a poorly cleaned bowel can mean repeating the test
- Call the clinic if you vomit the preparation or still pass brown stool by the morning
The morning of the test
Fasting and getting there
Stop eating and drinking at the times your instructions give, because you will be sedated. Bring your medicine list, any earlier reports and your insurance details. Arrange for an adult to take you home, because you must not drive for 24 hours after sedation.
- Take only the medicines you were told to take, with a small sip of water
- Wear comfortable clothes and leave jewellery at home
- Bring a companion, or arrange for one to collect you
After the colonoscopy
Going home and what is normal
You rest for a short while as the sedation wears off, then go home the same day with your companion. Bloating and wind are common and settle quickly. Severe abdominal pain, heavy bleeding, fever or vomiting are not normal: contact the clinic, or call 995 if you are very unwell.
- For 24 hours, do not drive, operate machinery, drink alcohol or sign important documents
- Most people eat normally afterwards unless told otherwise
- Results and any polyp tests are explained at your follow-up
About colonoscopy
What it finds, risks and recovery.
Colonoscopy cost
MOH benchmarks and MediSave.
Do I need screening?
A three-question check.
What else do people ask about preparation?
How do I know my bowel prep has worked?
When you are passing clear or pale yellow liquid with no solid pieces, the bowel is usually clean enough. If you are still passing brown stool close to the time of your test, call the clinic for advice.
Can I drink coffee or tea before a colonoscopy?
Many instructions allow black coffee or tea without milk as a clear fluid on the day before, but milk is not allowed. Your own instruction sheet is the one to follow, including when to stop all drinks before sedation.
What happens if my bowel is not clean enough?
Poor preparation can hide polyps, and the test may need to be repeated sooner or on another day. Finishing the whole preparation and keeping to the diet makes this much less likely.
Should I stop my blood thinner?
Not on your own. Whether to pause it depends on the medicine, why you take it, and whether polyps might be removed. The clinic gives a plan, sometimes after checking with the doctor who prescribed it.
Can I drive home after a colonoscopy?
No. Sedation affects your judgement and reactions, so you should not drive for 24 hours and an adult needs to take you home.
Sources
- NHS: Colonoscopy
- Sengkang General Hospital: Diet advice before colonoscopy
- Gut: BSG and ESGE guideline, endoscopy on antiplatelet or anticoagulant therapy (2021)
- American Society of Anesthesiologists: Multi-society GLP-1 guidance (2024)
- Gastrointestinal Endoscopy: ASGE/ACG quality indicators for colonoscopy (2024)