Please read this sheet carefully before your appointment and bring it with you on the day. If anything is unclear, contact the Endoscopy Unit before your procedure rather than on the day.

What is a colonoscopy?

A colonoscopy is an examination of the large bowel (colon) using a thin, flexible tube with a camera at its tip. The tube is passed gently through the back passage. The examination usually takes 20 to 45 minutes. If a growth (polyp) is found it can usually be removed during the same examination, and small tissue samples (biopsies) can be taken. Taking biopsies is not painful.

• 1 Caecum, where the colon begins (the test aims to reach here)
• 2 Ascending colon
• 3 Transverse colon
• 4 Descending colon
• 5 Sigmoid colon
• 6 Rectum and back passage (anus)
• 7 Colonoscope, the thin flexible tube with a camera

Illustration adapted from Servier Medical Art (smart.servier.com), licensed under CC BY 4.0.

Why has it been recommended for me?

Common reasons include bleeding from the back passage, a change in bowel habit, unexplained anaemia or weight loss, persistent diarrhoea or abdominal pain, bowel cancer screening and prevention, assessment of inflammatory bowel disease, and follow-up after polyp removal or a previous cancer.

What are the benefits?

Colonoscopy is the most accurate test for the lining of the large bowel, and the only one that both diagnoses and treats. Removing polyps before they become cancerous lowers your risk of bowel cancer, and a cancer found early can usually be treated successfully. A normal result is reassuring and often avoids further tests.

Preparing for the test: bowel cleansing

Bowel cleansing is the most important part of your preparation. Residue left in the colon hides the bowel lining, so polyps can be missed and the test may have to be repeated.

• Three days before: stop high-fibre foods — wholegrain bread and cereals, brown rice, nuts, seeds, dried fruit, raw fruit and vegetables, pulses and lentils.
• The day before: ideally no solid food all day. If you need to eat, have only a light low-fibre (low-residue) breakfast and lunch, and no solid food after lunch. Take clear fluids only, and aim for at least 2 litres.
• The bowel preparation solution given to you by the endoscopy staff: first dose on the evening before, second dose 4 to 6 hours before your appointment, finishing at least 2 hours before. Splitting the dose this way gives a much cleaner bowel than taking it all the night before. However, the final instructions are the ones given to you by the endoscopy staff who explained your bowel preparation. This timing does not apply if you are having a gastroscopy (OGD) together with your colonoscopy; follow the timing the endoscopy staff give you.
• Clear fluids allowed: water, clear tea or coffee without milk, clear soup or broth, strained apple juice, clear fizzy drinks. Avoid anything red or purple, and avoid milk or juices containing pulp.
• On the day: stop all fluids 2 hours before your appointment time.
• Stay close to a toilet once you start the preparation; frequent loose motions are expected. A barrier cream helps protect the skin.

Your medicines

• Blood thinners — warfarin, aspirin, clopidogrel, ticagrelor, prasugrel, rivaroxaban, apixaban, dabigatran, edoxaban: contact the unit at least 7 days before. Do not stop these on your own; stopping without advice can be dangerous.
• Iron tablets: stop 5 to 7 days before the test.
• Constipating medicines and anti-diarrhoeals (loperamide, codeine) and fibre supplements: stop 3 days before.
• Diabetes: tell the unit in advance. You will be given separate written instructions for your insulin or tablets.
• Weight-loss or diabetes injections (semaglutide, liraglutide, dulaglutide, tirzepatide): tell the unit, as extra instructions may be needed to reduce risk during sedation.
• All your other regular medicines: take them as usual with a sip of water, including on the morning of the procedure.

Sedation and your escort

Most patients are given a sedative and a painkiller through a vein. You will be drowsy and comfortable and will usually remember little of the test. You may also choose to have the examination without sedation.

If you have sedation you must be taken home by a responsible adult, and someone should stay with you for the rest of the day. For 24 hours afterwards do not drive, do not travel alone on public transport, do not operate machinery or cook, do not sign legal documents, do not drink alcohol, and do not care for young children on your own. Your procedure may be postponed if no escort is available.

On the day

Arrive at the time on your appointment card with your identification and a list of your medicines. The nursing team will check your details and complete the consent form with the doctor. You will change into a gown, a cannula will be placed in your arm, and your pulse, blood pressure and oxygen level monitored while you lie on your left side. Air or carbon dioxide is used to open up the bowel, so bloating and passing wind afterwards is normal. Tell the team at any point if you are uncomfortable — the test can be paused or stopped.

What are the risks?

Colonoscopy is a safe procedure. Serious complications affect about 1 to 4 people in every 1,000.

Are there alternatives?

CT colonography still needs bowel preparation, does not allow biopsies or polyp removal, and an abnormal finding usually means a colonoscopy is needed afterwards. Flexible sigmoidoscopy examines only the left side of the colon, and stool tests can suggest a problem but cannot exclude one. Choosing not to have the test is also an option; discuss with your doctor what might be missed.

After the procedure

You will rest in recovery for 30 to 60 minutes and can then eat and drink normally unless told otherwise. Bloating and mild cramps for a few hours are normal and relieved by walking. A small amount of blood with the first bowel motion is common after a biopsy or polyp removal.

The findings are explained before you leave and a written report is given. Because sedation affects memory, ask for the information to be repeated or given to the person accompanying you. Biopsy results take 2 to 4 weeks and are discussed in clinic. If a polyp was removed, keep the follow-up colonoscopy date you are given — repeating the test at the recommended interval is an essential part of preventing bowel cancer.

Contact

For appointments and questions, contact the endoscopy unit using the numbers it has given you. If you are seriously unwell, or it is outside working hours, go to the Emergency Department rather than waiting for a reply.

Based on NHS Bowel Cancer Screening Programme information and ASGE, ESGE and BSG/JAG colonoscopy standards. Supports but does not replace the discussion with your doctor and the consent process. PE-PROC-01 · v1.1 · October 2026 · Review: October 2028

This leaflet is general information and does not replace advice from your own doctor.