Procedure guide
Patient education · Reviewed by the treating clinician · Last reviewed January 2026
The quality of the preparation determines how much the endoscopist can see, and therefore how much the procedure can find. An inadequately prepared colonoscopy can miss polyps and early cancers, and frequently has to be repeated. This guide explains what to do and, importantly, why. Your own written instructions from the hospital take precedence if any detail differs.
What you are trying to achieve
The colon must be completely empty of stool, and the liquid that comes out should be clear or pale yellow by the time you arrive. Stool that remains in the bowel coats the lining and hides flat lesions, small polyps and early cancers. There is no way around this: the bowel has to be cleared.
Step 1: The low-fibre diet
Start the low-fibre diet for one to two days before the procedure, as instructed. Fibre lingers in the bowel because it is indigestible.
| Avoid | Choose instead |
|---|---|
| Whole grain bread, brown rice, bran, oats with husk | White bread, white rice, plain maida roti, plain rice porridge, upma without vegetables |
| Raw vegetables, salads, cabbage, cauliflower, carrot, corn, cucumber | Well-cooked, peeled vegetables such as boiled potato, bottle gourd, pumpkin (strained if needed) |
| Fruit skins, seeds, guava, custard apple, watermelon, grapes | Ripe banana, peeled soft apple or pear, strained fruit juice without pulp |
| Pulses, rajma, chana, sprouts, soya | Clear strained dal water, plain khichdi without vegetables |
| Nuts, seeds, popcorn, coconut, dry fruits | None on the day before |
| Milk, curd, buttermilk, cheese | Clear liquids only from the afternoon before |
Stop iron tablets
Iron makes the stool black, hard and difficult to clear. It is usually stopped about seven days before. If you take iron for anaemia, confirm with the hospital when booking. Do not stop any heart, blood pressure or other essential medicine unless specifically told to.
Step 2: Clear liquids only
From the time instructed — usually the afternoon before — take only clear liquids. “Clear” means you can see through them.
- Water, plain soda water.
- Clear soup (strained, no pieces of vegetable or noodles).
- Clear fruit juice without pulp — apple, white grape, coconut water.
- Black tea or coffee without milk.
- Oral rehydration solution or electrolyte drinks.
- Plain jelly or clear ice lollies, without colouring if possible.
Avoid anything red, purple, dark blue, black or dark brown — including grape juice, beetroot, tomato soup and coloured jelly. These can be mistaken for blood and can obscure the view.
Do not skip fluids
Preparation causes significant fluid loss. Keep drinking clear fluids regularly throughout the day. Dehydration is one of the commonest reasons people feel unwell during preparation, and it is entirely preventable.
Step 3: The bowel-preparation solution
The solution works by drawing water into the bowel, flushing it out. Timing is critical, and the split-dose schedule matters because it clears the part of the colon that is hardest to reach — the right side — close to the time of the procedure.
- Half the solution the evening before, taken over about an hour or two as instructed.
- Half the solution on the morning of the procedure, usually about four to six hours before your appointment.
Practical tips that make a real difference:
- Chill the solution. It is much easier to drink cold.
- Sip steadily rather than drinking large volumes at once, which causes nausea.
- Suck a slice of lemon or a boiled sweet between glasses to mask the taste — but avoid red or purple sweets.
- Keep moving gently. Walking around helps the solution work and reduces bloating.
- Stay close to a toilet once it starts working. It acts within about 30–60 minutes.
- Apply a barrier cream to reduce soreness from the repeated passage of stool.
Step 4: Know when to stop eating and drinking
Follow the fasting instruction exactly. Usually nothing at all by mouth for the last few hours before the procedure — the exact cut-off will be given in writing. This matters both for the quality of the view and for your safety under sedation.
When to call the hospital before you arrive
- Your bowel movements are still brown or contain solid material when you are due to leave home.
- You are vomiting and cannot keep the solution down.
- You develop severe abdominal pain, marked abdominal swelling or a fever.
- You feel faint, dizzy or very weak, or you cannot keep fluids down.
- You have not passed urine for many hours.
In almost all these situations it is better to call and adjust the plan than to proceed with a poor preparation or an unsafe one.
Diabetes medicines and insulin
Because the preparation involves fasting, diabetes medicines usually need adjustment. Some tablets should be held, and insulin doses are typically reduced. Certain diabetes medicines in particular must be stopped before bowel preparation for safety reasons. This must be planned in advance with the doctor who manages your diabetes, or by us if you tell us at booking.
Blood thinners
If you take warfarin, apixaban, rivaroxaban, dabigatran, edoxaban, clopidogrel or similar, tell us at the time of booking. Whether these need to be paused, and for how long, depends on why you take them and whether polyps are likely to be removed. Do not stop them yourself without advice, and do not continue them without telling us.
The most common preparation mistakes
- Starting the diet too late. One day of diet is usually not enough; two days is better.
- Not drinking enough clear fluid. Leads to dehydration and a poor flush.
- Taking the second dose too early. The right side of the bowel refills, and lesions there are missed.
- Continuing iron tablets. Makes the stool black and hard to clear.
- Eating “just a little” solid food. Even a small amount leaves residue.
- Not telling the hospital about diabetes or blood thinners. This can be genuinely unsafe.
- Assuming brown liquid output is fine. It is not — clear or pale yellow is the target.
What “good preparation” looks like
By the time you leave for the hospital, the liquid you pass should be clear, pale yellow or light green, with no solid particles and no brown colouring. If it is, the endoscopist should be able to see the entire lining of the bowel. If it is not, please say so — telling us before the procedure is far better than discovering it during.
Please remember
This article is general health information, not personal medical advice. It cannot account for your individual circumstances. Do not start, stop or change any medicine based on it. If you are worried about your symptoms, please book a consultation, and in an emergency seek care immediately.