What happens during a colonoscopy, and what should you expect?

Colonoscopy is one of the most valuable diagnostic tools available in bowel medicine, yet it is a procedure that many patients feel anxious about. In my experience, most of that anxiety comes from not knowing what to expect. Here I want to walk you through exactly what happens, before, during, and after, so that you can approach it with confidence.

What is a colonoscopy?

A colonoscopy is a procedure to examine the lining of the entire large bowel using a colonoscope: a thin, flexible tube with a camera and light at its tip. It allows me to look directly at the bowel wall, identify any abnormalities, take biopsies, and in many cases treat conditions such as polyps at the same time.

Preparation

The day before your colonoscopy, you will be asked to follow a low-residue diet and take a bowel preparation solution to clear the bowel completely. This is essential. A clean bowel allows a thorough examination and reduces the risk of missing anything important. You will receive written instructions in advance detailing exactly what to eat and drink and when to take your preparation. It is important to follow these carefully.

On the day

You should arrange for someone to drive you home, as sedation is used for the procedure. On arrival, a member of the clinical team will check your details, take a brief history, and answer any questions. A cannula is placed in the back of your hand to administer the sedation. The sedation used is conscious sedation; you will feel relaxed and drowsy but will remain able to respond if needed. Most patients have little or no recollection of the procedure afterwards.

During the procedure

The colonoscope is gently passed through the anus and advanced around the entire large bowel to the point where it joins the small bowel. Air or carbon dioxide is used to inflate the bowel slightly, which allows a clear view of the lining. The procedure typically takes between 20 and 45 minutes, depending on the complexity of the examination and whether any treatment is carried out. If polyps are found, they can usually be removed at the same time using a technique called polypectomy. Biopsies can be taken of any areas that look abnormal.

After the procedure

You will recover in a dedicated recovery area until the sedation has worn off, usually within 30 to 60 minutes. I will come and speak with you before you leave to discuss the findings and any immediate next steps. A written report is provided, and further results, such as biopsy reports, are typically available within one to two weeks. Most patients feel entirely well by the following day. Some mild bloating or discomfort is normal and settles quickly.