Colonoscopy: Preparation, Procedure, and Recovery Basics

A colonoscopy is an examination of the large bowel using a thin, flexible tube with a camera. It is commonly used to investigate symptoms such as bleeding from the rectum, changes in bowel habits, unexplained anaemia, or ongoing abdominal problems. It is also used for bowel cancer screening and for follow-up in some digestive conditions. For anyone looking to better understand procedures like this, our Examinations and Treatments Explained for Patients guide provides a helpful overview of medical tests.

For many people, the main questions are how to prepare, what happens during the test, and what is normal afterwards. This guide explains when a colonoscopy may be recommended, how bowel preparation usually works, what to expect on the day, and which symptoms after the procedure should prompt medical advice.

When doctors recommend a colonoscopy

A doctor may recommend a colonoscopy when there is a need to look directly at the lining of the colon and rectum. The test can help find the cause of symptoms, check abnormal results from other tests, remove polyps, or take small tissue samples called biopsies.

Common reasons include:

• blood in the stool or bleeding from the rectum
• a persistent change in bowel habits, such as ongoing diarrhoea or new constipation
• unexplained iron deficiency anaemia
• long-lasting abdominal pain, bloating, or unexplained weight loss
• a positive stool screening test for hidden blood
• surveillance after previous bowel polyps
• assessment or follow-up of inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease affecting the colon

It may also be recommended as part of a bowel cancer screening programme, especially for people above a certain age or with a higher personal risk. A stronger family history of colorectal cancer or certain inherited syndromes may lead to earlier or more frequent colonoscopy, depending on specialist advice.

Not every bowel symptom requires a colonoscopy. In some situations, a doctor may first consider stool tests, blood tests, sigmoidoscopy, CT colonography, or other investigations. The most appropriate test depends on age, symptoms, medical history, and the level of concern for conditions such as polyps, cancer, inflammation, or diverticular disease.

How to prepare for a colonoscopy

Good bowel preparation is one of the most important parts of a successful colonoscopy. If stool remains in the bowel, the camera view can be unclear and small polyps or areas of inflammation may be missed. In some cases, the test has to be repeated if the bowel is not clean enough.

Diet and fluid instructions

The exact instructions vary by hospital or endoscopy unit, so the written guidance provided for the appointment should be followed carefully. In many centres, patients are asked to switch to a low-fibre diet for one or more days before the procedure and then move to clear fluids the day before. You can also find additional tips on preparing for medical tests effectively at home to help make your experience smoother.

Clear fluids often include water, tea or coffee without milk, clear soup, and some non-red clear drinks. Red or purple drinks are sometimes avoided because they can look like blood during the examination. Good hydration is important because the bowel-cleansing solution can cause significant fluid loss through frequent diarrhoea.

Bowel-cleansing medication

Most patients need a laxative preparation designed to empty the colon. This is often taken in split doses, with part taken the day before and part taken several hours before the procedure. Split dosing usually improves bowel cleansing and may increase the chance of a complete examination.

After starting the preparation, bowel motions usually become frequent, loose, and then watery. Staying close to a toilet is usually necessary. Applying a barrier cream around the anus may help reduce irritation from repeated wiping.

Medicines that may need special review

Some medicines need extra planning before a colonoscopy, especially if a biopsy or polyp removal may be needed. Important examples include:

• blood thinners such as warfarin, apixaban, rivaroxaban, dabigatran, or clopidogrel
• diabetes medicines, including insulin
• iron tablets, which may need to be stopped in advance
• some medicines that affect kidney function or fluid balance

These medicines should not be stopped without professional advice. The plan depends on why the medicine is used, the dose, and the expected type of colonoscopy.

Practical preparation for the day

• Check when to stop eating and drinking.
• Ask whether sedation is planned or optional.
• Arrange for someone to accompany you home if sedation is being used.
• Bring a list of your regular medicines and allergies.
• Wear loose, comfortable clothing.

If the bowel preparation causes vomiting, severe dizziness, inability to keep fluids down, or very little urine output, the endoscopy unit or medical team should be contacted, as dehydration can become a problem.

What happens during a colonoscopy procedure

A colonoscopy is usually done in an endoscopy unit or a hospital day-case setting. Before the procedure, a nurse or doctor typically reviews symptoms, medicines, allergies, and consent. A small plastic cannula may be placed in a vein if sedative or pain-relief medicine is planned.

During the examination, the patient usually lies on their side while the colonoscope is passed through the anus and guided through the rectum and colon. The instrument is thin and flexible, with a light and camera at the tip. Small amounts of air or carbon dioxide are used to open the bowel so the lining can be seen clearly.

The procedure may be done:

• without sedation
• with light sedation
• with pain relief and sedation together, depending on local practice and the individual situation

People experience the test differently. Some feel mainly pressure, bloating, and cramping as the scope moves around bends in the bowel. Others feel only mild discomfort, especially if carbon dioxide is used, as it is absorbed more quickly than room air. Previous abdominal surgery, a very looping colon, diverticular disease, or active inflammation can make the procedure more uncomfortable or technically difficult in some cases.

Biopsies and polyp removal

If an abnormal area is seen, the doctor may take biopsies using tiny instruments passed through the scope. This is usually not felt. Polyps can often be removed during the same procedure, which is one reason colonoscopy is important not only for diagnosis but also for prevention of colorectal cancer.

The test often takes around 20 to 45 minutes, but this can vary. More time may be needed if the bowel is difficult to navigate, if cleaning is required during the procedure, or if several polyps need to be removed.

After the examination room

If sedation was used, monitoring during a short recovery period is common. The final report may be discussed on the same day, but biopsy results usually take longer. If sedation was given, driving, cycling, signing important documents, drinking alcohol, or returning to certain types of work may need to be avoided until the next day, depending on local advice.

What is normal after a colonoscopy

After a colonoscopy, it is common to feel bloated, pass wind, or have mild cramping for a few hours. This usually happens because air or carbon dioxide was introduced into the bowel during the test. A small amount of blood on toilet paper or with the first bowel movement can also happen, especially if biopsies were taken or a polyp was removed.

Normal short-term effects may include:

• mild abdominal discomfort or fullness
• passing gas more than usual
• sleepiness, poor concentration, or mild nausea after sedation
• a slight sore feeling around the anus after repeated bowel motions from the preparation
• a temporary change in bowel habit for a day or two

Most people can eat again after the procedure unless they are told otherwise. Starting with light meals and drinking enough fluid can help, especially if the bowel preparation caused dehydration. If a larger polyp was removed, there may be specific temporary restrictions on diet, travel, exercise, or medication.

Results also vary. Some patients are told the colonoscopy was normal. Others may be found to have haemorrhoids, diverticulosis, inflammation, polyps, or other changes that need follow-up. A normal colonoscopy does not rule out every cause of symptoms, but it can be very reassuring in many situations.

When to contact a doctor after a colonoscopy

Serious complications after colonoscopy are uncommon, but they can occur. Medical advice should be sought promptly if symptoms suggest significant bleeding, infection, or a tear in the bowel wall, called perforation.

Contact a doctor or seek urgent medical care if there is:

• severe or worsening abdominal pain, especially if the abdomen becomes hard or swollen
• heavy rectal bleeding, repeated bleeding, or large blood clots
• fever, chills, or feeling markedly unwell
• vomiting that continues or inability to keep fluids down
• dizziness, fainting, weakness, or signs of dehydration
• chest pain or breathing difficulty after sedation

A small amount of bleeding can be normal after biopsy or minor polyp removal, but ongoing or increasing bleeding is not. Delayed bleeding can also happen several days after removal of a larger polyp, so instructions given at discharge should be followed carefully.

If biopsies were taken or polyps removed, it is sensible to understand when results are expected and who will explain them. Follow-up may involve the referring doctor, a gastroenterology clinic, or a colorectal specialist, depending on what was found.