In short: A colonoscopy is a hospital test in which a thin, flexible tube with a camera is passed into the bottom to look at the lining of the large bowel. It is used to investigate symptoms such as bleeding from the bottom or a lasting change in bowel habit, and to follow up an abnormal bowel screening result. Polyps can often be removed during the test. In England, routine bowel screening for people aged 50 to 74 uses a home stool test (FIT) every two years, not a routine colonoscopy.

This guide, reviewed by a Ready Health prescribing pharmacist, explains why a colonoscopy is done, how to prepare, what it feels like and what happens afterwards.

What is a colonoscopy?

During a colonoscopy, a specialist (an endoscopist) guides a colonoscope through the rectum and around the colon. The camera sends images to a screen, so the bowel lining can be checked in detail. Small tissue samples (biopsies) can be taken and most polyps can be removed at the same time.

Why might I need a colonoscopy?

A colonoscopy may be recommended to investigate or monitor:

Bleeding from the bottom or blood in your poo.
A persistent change in bowel habit, such as looser or more frequent stools.
Unexplained weight loss, tummy pain or a lump in the abdomen.
Iron deficiency anaemia without a clear cause.
A positive FIT (faecal immunochemical test) result, either from NHS bowel screening or a test arranged because of symptoms.
Inflammatory bowel disease, such as Crohn's disease or ulcerative colitis.
Follow-up after previous polyps, or a strong family history of bowel cancer, as advised by a specialist.

If you have symptoms such as bleeding, a change in bowel habit for three weeks or more, or unexplained weight loss, see your GP. Most people with these symptoms do not have cancer, but they should always be checked.

How does bowel cancer screening work in England?

Who	What is offered
Age 50 to 74, registered with a GP	A free home FIT kit by post every two years
Age 75 and over	You can request a kit by calling the free bowel screening helpline
Abnormal FIT result	Appointment with a specialist screening practitioner, usually followed by colonoscopy

Screening arrangements differ slightly in Scotland, Wales and Northern Ireland.

How do I prepare for a colonoscopy?

Your bowel needs to be empty so the lining can be seen clearly. The hospital will give you written instructions, which you should follow exactly. Typically:

You follow a low-fibre diet for a day or two beforehand.
You take a strong laxative ("bowel prep") the day before and sometimes on the morning of the test, which causes frequent watery bowel movements, so stay near a toilet.
You may need to stop iron tablets and adjust some medicines. If you take blood thinners, diabetes medicines (including insulin or GLP-1 medicines) or the contraceptive pill, ask the endoscopy team for advice, as bowel prep can affect how they work.

What happens during a colonoscopy and does it hurt?

You lie on your side and are usually offered a sedative and painkiller through a vein, or gas and air. You stay awake but more relaxed. Air or carbon dioxide is used to open up the bowel, which can cause cramping and bloating. Most people find it uncomfortable rather than painful. The test usually takes around 30 to 45 minutes.

What happens after a colonoscopy?

If you had sedation, someone must take you home and stay with you, and you should not drive, drink alcohol, operate machinery or sign legal documents for 24 hours.
Wind and bloating usually settle within a few hours.
You may be told some findings straight away; biopsy results usually take a few weeks.

Colonoscopy is generally safe, but like any procedure it has risks, including bleeding (more likely if polyps are removed), a reaction to sedation, and, rarely, a tear (perforation) in the bowel. Seek urgent help if you develop severe tummy pain, a fever, or heavy or ongoing bleeding afterwards.

Frequently asked questions

Do I need a colonoscopy at 50?

Not routinely in the UK. People aged 50 to 74 in England are offered a home FIT test every two years. Colonoscopy is for people with symptoms, a positive FIT, or specific higher risk.

Are there alternatives to colonoscopy?

Sometimes. Options include CT colonography (a specialised CT scan) or flexible sigmoidoscopy, which looks at the lower bowel only. The specialist will advise which is right for you.

Can I go back to work the next day?

Most people can, unless they are told otherwise.

Can I arrange a colonoscopy privately?

Yes, private colonoscopy is available at independent hospitals, usually after a consultation with a specialist who decides whether it is the right test.

Key takeaways

A colonoscopy examines the large bowel with a camera and can remove polyps.
Symptoms like rectal bleeding or a lasting change in bowel habit should be checked by a doctor.
NHS bowel screening in England uses a home FIT kit every two years from age 50 to 74.
Good bowel preparation and following medicine advice make the test more accurate and safer.

Sources and further reading

Last reviewed: October 2026 by Shamir Patel, Independent Prescribing Pharmacist, Ready Health. This article is general information and does not replace advice from your own clinician.

Worried about bowel symptoms or want help accessing specialist care? Ready Health in Standish, Wigan, can offer a consultation, arrange blood tests where appropriate, and discuss private medical referrals to a specialist. For new or worrying symptoms, you can also contact your NHS GP.