Colonoscopy Procedure

Understanding Your Colonoscopy

A colonoscopy allows your gastroenterologist to examine the lining of your large bowel using a flexible viewing instrument called a colonoscope. This thin tube, equipped with a small video camera at its tip, passes through the rectum to provide a clear view of your colon’s interior. During the examination, your doctor can identify problems, take tissue samples for laboratory analysis, and remove abnormal growths when appropriate.

Why Your Doctor has Recommended this Procedure

Your gastroenterologist may recommend colonoscopy to investigate symptoms or screen for disease. The procedure can identify polyps, areas of inflammation, and cancerous changes within the bowel. It proves particularly valuable when investigating unexplained symptoms such as altered bowel habits, rectal bleeding, abdominal discomfort, or unintended weight loss.

For patients with a family history of colorectal cancer, regular colonoscopy forms an important part of preventive care and may help detect problems before they develop into more serious conditions.

How Polyps Develop into Cancer

The bowel lining normally consists of healthy cells that grow and divide in an orderly manner. Sometimes abnormal cells form small growths called polyps, which protrude from the bowel wall. While most polyps remain harmless, a small proportion gradually develop changes that can lead to cancer. When abnormal cells multiply unchecked, they eventually form a tumour that may grow through the bowel wall. Removing polyps during colonoscopy effectively interrupts this progression and provides significant protection against bowel cancer.

Preparing Your Bowel for Examination

Thorough bowel preparation makes all the difference between a successful examination and one that must be repeated. Your doctor needs a completely clear view of the bowel lining, which is only possible when all waste material has been removed. This requires careful attention to dietary restrictions, taking the prescribed bowel preparation, and maintaining adequate fluid intake.

Adjusting What You Eat

Several days before your procedure, you will need to modify your diet according to the specific instructions provided by your doctor’s rooms. Most preparation protocols require avoiding foods that contain seeds, grains, or high fibre content, as these can obstruct the colonoscope’s working channels and interfere with the examination.

Taking Your Bowel Preparation

Your doctor will prescribe a bowel preparation medication that causes diarrhoea to empty your colon. Several different preparations are available, and your doctor will select the most appropriate option based on your individual medical circumstances. Following the instructions exactly as written ensures the preparation works effectively. An inadequately prepared bowel may require you to repeat the entire process on another day.

Maintaining Your Fluid Intake

The bowel preparation process removes significant fluid from your body. You must drink the recommended amounts of clear fluids to prevent dehydration and help the preparation work properly. Your doctor’s instructions will specify which fluids are appropriate and how much you should consume.

Managing Your Regular Medications

Certain medications require adjustment before colonoscopy. You must inform your doctor about all medicines, vitamins, and supplements you take regularly, including those available without prescription.

Iron supplements typically need to cease one week before the procedure. If you take anti-inflammatory medications or fish oil supplements for conditions such as arthritis, these should stop five days beforehand.

Blood-thinning medications require particularly careful management. Medicines such as warfarin, clopidogrel, apixaban, rivaroxaban, and dabigatran may need to be ceased for several days or weeks before your procedure. Your doctor will discuss the appropriate timing with you, weighing the risks of stopping these medications against the needs of the procedure.

Patients taking medications with names ending in ‘gliflozin’ should cease these three days before the procedure. These diabetes medications carry specific risks during bowel preparation.

If you use GLP-1 receptor agonist injections such as semaglutide (Ozempic®, Wegovy®) or tirzepatide (Mounjaro®) for diabetes or weight management, you must notify your doctor. These medications affect how quickly the stomach empties and require special consideration before colonoscopy.

For patients with diabetes, medication adjustments help maintain stable blood sugar levels during the fasting period and procedure. Your doctor will provide specific guidance about modifying tablets and insulin to keep you safe.

What Happens During Your Colonoscopy

Sedation and Comfort

The procedure typically takes between 20 and 45 minutes to complete. Before the examination begins, you will receive medication through a vein to make you comfortable. This sedation allows you to relax deeply during the procedure. While you may have vague awareness of activity in the room, most patients remember little or nothing about the examination itself. Throughout the colonoscopy, staff will monitor your breathing, heart rate, and blood pressure to ensure your safety.

Examining Your Bowel

Once adequately sedated and positioned on your left side, your doctor will gently pass the colonoscope through the anal opening into your colon. The camera transmits images to a video screen, allowing detailed inspection of the bowel lining. Your doctor will carefully advance the instrument to the point where your small intestine joins the colon, then withdraw it slowly while examining the lining thoroughly.

Taking Samples and Removing Polyps

When your doctor identifies a polyp during the examination, it will usually be removed. Polyps are growths that develop on the bowel wall. Most prove entirely benign, but because a small proportion carry the potential to become cancerous over time, removing them provides important protection. Your doctor may also take small tissue samples called biopsies from areas that require microscopic examination.

After Your Procedure

Following colonoscopy, you will rest in the recovery area for one to two hours while the sedation wears off. Once fully awake, you will be offered something to eat and drink.

Some bloating is common after the procedure due to air used to inflate the colon during the examination to provide clear views of the bowel lining. This discomfort typically resolves within an hour or two. Occasionally, you may notice a small amount of rectal bleeding, particularly if biopsies were taken. This usually settles quickly without treatment.

The sedation used during colonoscopy affects your judgement and coordination for the rest of the day. You must not drive, use public transport alone, operate machinery, sign legal documents, or consume alcohol for 12 hours after the procedure and until you have had a normal night’s sleep. You must arrange for a responsible adult to take you home and remain with you. Most patients feel completely recovered by the following day. Please read your discharge instructions carefully before leaving.

Understanding the Risks

Colonoscopy performed by appropriately trained gastroenterologists is very safe. Serious complications occur rarely, though no medical procedure is entirely without risk.

The likelihood of complications depends on several factors, including the specific interventions performed during your examination and your general health. Very rarely, the colonoscope may cause a tear in the bowel wall. This occurs in approximately one in 1,000 examinations and requires hospital admission for surgical repair.

Some patients experience headaches or nausea from the bowel preparation medication. Reactions to sedation medications are possible but uncommon. In a small number of cases, technical difficulties may prevent complete examination, necessitating a repeat procedure.

When to Seek Medical Attention

Contact your doctor’s rooms or the hospital immediately if you experience any of these symptoms in the two (2) weeks following colonoscopy:

• Severe pain in your abdomen
• Black or tarry bowel motions
• Continued bleeding from the rectum
• Fever or chills
• Any other symptoms causing concern

How Accurate is Colonoscopy?

Colonoscopy provides the most reliable method available for examining the colon. However, no test achieves perfect accuracy. Small polyps may occasionally be missed, with studies suggesting this occurs in approximately 2 to 8 per cent of examinations. Larger abnormalities, including cancers, are missed much less frequently, though the possibility remains.

Because of these limitations, screening programs remain important even for patients who have had colonoscopy. The National Bowel Cancer Screening Program provides faecal occult blood (FOB) test kits to eligible Australians. These tests detect blood in bowel motions that may indicate the presence of polyps or cancer. You should participate in this programme and perform testing every one to two years as recommended. Test kits are available from your local pharmacy or general practitioner.

Infection Control and Instrument Sterilisation

Between each use, the colonoscope and all associated instruments undergo thorough cleaning and disinfection according to strict protocols. These procedures eliminate any risk of transmitting infections such as HIV or hepatitis between patients. Your gastroenterologist follows guidelines established by the Gastroenterological Society of Australia (GESA) to ensure your safety.

Questions About Your Procedure

If you have questions or concerns about any aspect of your colonoscopy, please contact your doctor’s rooms before your appointment. Your gastroenterologist and their staff are available to provide the information you need to feel prepared and confident about your procedure.

Related procedures include reflux, gastroscopy (upper endoscopy), oesophageal manometry, 24-hour pH monitoring, endoscopic dilation, and anti-reflux surgery (fundoplication).

This information has been adapted from patient education resources developed by the Gastroenterological Society of Australia (GESA).

Last reviewed: 5 December 2025