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Before your endoscopy

Fasting and Bowel Prep — Before an Endoscopic Biopsy

Most people find the preparation harder to get through than the procedure itself. This page tells you exactly what the preparation involves, so you know what to expect before you start.

Medically reviewed by Dr. Mohammed Imaduddin, Surgical Oncologist, MBBS · MS (General Surgery) · M.Ch (Surgical Oncology) · Last reviewed September 2026

  • Upper and lower scope are different — Upper endoscopy needs only a fast. Lower endoscopy also needs a bowel prep solution the day before.
  • Your instruction sheet is the one to follow — General advice online may not match your specific procedure. Your team's written instructions take priority.
  • The prep solution is the hardest part — It tastes unpleasant and the laxative effect is significant — but there are practical ways to make it easier.
  • Incomplete prep means rescheduling — Arriving without adequate preparation is the most common avoidable reason a procedure has to be abandoned.
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How long you need to fast depends on whether your endoscopy looks at the upper or lower digestive tract. For upper endoscopy, the instruction is usually nothing to eat or drink from midnight. Lower endoscopy also needs a bowel prep laxative the day before. Your written instruction sheet from your team is the one to follow.

What do I need to do to prepare for my endoscopic biopsy?

  1. Read your written instruction sheet first

    Your team will give you a printed sheet specific to your procedure. Upper and lower endoscopy have different requirements. Follow your sheet — it tells you your fasting time, which medicines to pause, and whether you need a prep solution.

  2. Adjust your diet the day before (lower scope only)

    If your procedure looks at the lower bowel, you may be asked to eat only low-fibre foods during the day, then move to clear liquids by early evening. Your instruction sheet will say which foods are allowed. This step does not apply to upper endoscopy.

  3. Take the prep solution (lower scope only)

    Bowel prep is a laxative solution you drink to clear the colon. You will usually take it the evening before, or in two doses — one the evening before and one the morning of the procedure. Plan to stay near a toilet for several hours after starting it.

  4. Fast from midnight

    For most endoscopic procedures, nothing to eat from midnight. Some instructions also ask you to stop drinking at a specific time. If your sheet says you can take morning medicines with small sips of water, follow that instruction.

  5. Tell your team what medicines you take

    Blood thinners and diabetes medicines in particular may need to be adjusted around the procedure. Bring a full written list of everything you take. Do not stop any medicine on your own without asking.

  6. Arrange transport home and arrive on time

    You will not be able to drive yourself home after the procedure. Arrange for someone to collect you before the day. Arrive at the time your team has given you — recovery and check-in are built into the schedule.

What should I bring on the day?

  • Your printed instruction sheet and any medicines your team has asked you to bring
  • A written list of all medicines you take, including supplements and herbal remedies
  • Someone to take you home — you cannot drive after the procedure
  • Comfortable, loose clothing that is easy to change out of
  • Details of any allergies, especially to medicines or latex
  • Confirmation that you have fasted for the time stated on your instruction sheet

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What is the bowel prep and why does it matter?

Bowel prep is a laxative solution that flushes the colon clear of stool. For the endoscopist to see the bowel wall clearly enough to take a biopsy, the colon must be clean. Incomplete preparation means the procedure may need to be stopped and rescheduled.

The solution tastes unpleasant to most people. Chilling it beforehand, drinking it through a straw, or following each glass with a small amount of clear juice can make it easier. Your instruction sheet may suggest specific tips.

The laxative effect starts within a couple of hours and can be intense. Plan to stay at home, close to a toilet. You are not unwell — this is the preparation working as it should.

What if I cannot finish the bowel prep solution?

Call your team as early as possible — not on the morning of the procedure if you can avoid it. They will tell you whether to continue, slow down, or reschedule. Do not decide on your own to skip it and come in anyway.

If nausea is stopping you, pausing briefly before continuing can help. Taking the solution more slowly, or in smaller amounts, also helps some people. Ask your team whether an anti-nausea measure is appropriate for you.

Arriving without adequate preparation is the most common avoidable reason a lower endoscopy is abandoned partway through. Telling your team early is always the better option.

Did you know?

Incomplete bowel preparation is the most common avoidable reason a lower endoscopy has to be abandoned or rescheduled.

Gastroenterology guidelines identify preparation quality as the single factor most under the patient's control — not the complexity of the procedure itself.

Source: British Society of Gastroenterology: Quality Indicators for Colonoscopy

Explore 62 more Biopsy Techniques and How They Compare topics

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Common questions

Frequently asked questions

Do I still need to fast if I am only having an upper endoscopy?

Yes. Having food or liquid in the stomach during an upper scope creates a risk of inhaling material if sedation affects your swallow reflex. Nothing to eat from midnight is the standard instruction, and your team may ask you to stop fluids at a specific time as well. You do not need to take a bowel prep solution for an upper endoscopy — that is only required when the lower bowel is being examined.

Which medicines should I pause before an endoscopic biopsy?

Blood thinners, diabetes medicines and insulin, and some blood pressure medicines are the ones most commonly adjusted around endoscopic procedures. Which applies to you depends on your specific medicines, your procedure, and your other health conditions. Bring a full written list to your pre-procedure appointment and ask your team directly about each one. Never stop a medicine on your own judgement before asking.

Why does the bowel prep solution taste so bad — is there a better option?

Different solutions are available, and some are lower in volume or better tolerated than others. Which one your team prescribes depends on factors including your kidney function and what is clinically appropriate for your procedure. If you found a previous preparation very difficult to tolerate, tell your team before the preparation day — not on the day itself. They may be able to offer an alternative.

I have diabetes. What do I do about fasting and bowel prep?

Fasting and bowel prep both affect blood sugar, and the standard fasting instructions do not apply to people with diabetes without adjustment. Tell your team you have diabetes at the time of booking, not on the day. They will give you specific instructions about when to take your medicines and how to monitor your glucose during the preparation period.

What if I accidentally eat or drink something during the fasting period?

Tell your team before you arrive — not on arrival. Depending on what you had and when, the procedure may need to be postponed. Arriving without telling them creates a safety risk, because the reason for the fast is to reduce the risk of complications with sedation. Your team would rather reschedule than proceed unsafely, and they will not penalise you for being honest.

How long will I be at the centre on the day?

The procedure itself is usually completed within 20 to 45 minutes depending on what is being done, but you should plan to be at the centre for several hours in total. Check-in, changing, the procedure, and recovery time before your team is satisfied you are safe to leave all add up. If sedation is used, it takes time to wear off fully. Your team will give you a realistic estimate for your specific procedure.

Full index

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