Colonoscopy side effects

Colonoscopy side effects: what is common and when to react

Colonoscopy is usually completed without a serious complication, but risk depends in part on whether biopsies are taken or polyps removed and on your other conditions and medication. This page explains which effects are usually mild and passing, and which symptoms need same-day assessment by the clinic or out-of-hours services (1813 in the Capital Region, otherwise your local out-of-hours doctor).

Common, usually mild and passing effects

In the first hours and the first day after the colonoscopy you may notice:

• abdominal cramping and mild bloating from the air or carbon dioxide (CO2) introduced into the bowel. Carbon dioxide is absorbed faster than ordinary air and usually causes less bloating
• urge to burp and passing of wind, which eases as the gas comes out
• a small amount of fresh blood in the stool if polyps were removed or biopsies taken
• tiredness from the sedation and from the bowel preparation
• loose or no bowel motions for 1–2 days because the bowel has been emptied

These effects usually ease during the first day. Rest and drink as needed. If they get worse rather than better, or you develop any of the symptoms under "When to call", seek assessment.

Side effects from the bowel preparation

The bowel prep is, for most people, the most unpleasant part of a colonoscopy pathway. Watery diarrhoea, cramps, nausea and headache are common, and many feel washed out the next day. Redness around the anus is eased with a thick barrier cream. Drink clear fluids according to the plan you were given to replace the fluid lost during preparation. Sugary drinks alone do not replace the salts the body loses; follow the clinic's advice on what to drink, especially if you have heart or kidney disease, a fluid restriction or diabetes.

Side effects from sedation

If you are given sedative or pain-relieving medication during the procedure (this is agreed with the clinician based on need and health), you may notice:

• drowsiness and mild dizziness for 4–6 hours
• a transient memory gap around the procedure itself, a known effect of the medication
• mild nausea

If you have received intravenous sedation, then for 24 hours you must not drive, cycle, operate machinery, drink alcohol, sign legally binding documents or make important decisions. An adult should accompany you home.

Rare but serious complications

Serious complications are rare. The risk depends among other things on whether polyps are removed, on their size and the technique used, and on your other illnesses and medication. It is important to know the symptoms, because early contact decides how quickly we can treat:

• Bleeding from a polyp removal site. A little fresh blood the first time you go to the toilet is common. Larger amounts of red blood, clots or bleeding that continues need to be assessed. Bleeding can also occur up to one to two weeks later, when the scab comes loose
• Perforation (a hole in the bowel wall). Serious but rare. The risk depends among other things on whether polyps were removed and on the size of the lesion. Symptoms are severe persistent abdominal pain, a hard distended abdomen, fever and chills. In rare cases a hole only becomes apparent some days after the examination
• Post-polypectomy syndrome. A heat injury to the bowel wall after polyp removal with electrical current, without an actual hole. It causes abdominal pain, tenderness and possibly fever within the first days and can resemble a perforation, so you need to be examined
• Infection. Symptoms are fever, chills and feeling generally unwell in the days afterwards
• Reaction to sedation. Breathing difficulty or unusually heavy drowsiness during the clinic visit itself. We monitor you throughout

When to call

Call 112 immediately for breathing difficulty, chest pain, heavy rectal bleeding that does not stop, or feeling seriously unwell. These can be signs of a serious complication that needs emergency hospital treatment.

Seek assessment the same day. Do not wait for the clinic to open. Call the clinic during opening hours on +45 39 64 01 25, otherwise the acute helpline (1813 in the Capital Region of Denmark, otherwise your local out-of-hours service), if you experience:

• increasing or severe abdominal pain, especially if the abdomen becomes hard and distended
• heavier or repeated bleeding from the bowel
• fever, chills or feeling generally unwell
• vomiting that will not stay down

Mild tiredness or feeling slightly off on its own is not a reason to call 112, but if in doubt, call 1813 or your out-of-hours service for advice.

Timeline: what you feel and when

When	What is common	When to seek help
First hour	Bloating, urge to burp	Severe pain, not just discomfort
Rest of the day	Tiredness, mild nausea from sedation	Breathing difficulty
First 24 hours	Loose or no stool, a little blood after polyp removal	Persistent or heavy bleeding
Days 2–3	Bowel motions often start to return to normal, but the timing varies	Fever, chills, increasing abdominal pain
Up to 2 weeks	Quiet course	Late-onset pain or bleeding when the scab after polyp removal comes loose

Fewer side effects next time

The risk is assessed individually before the procedure and depends among other things on whether polyps are removed and on your other medication. We always review your medication before the procedure and agree an individual plan with you for the time before and after. Never stop or change prescribed medication without a specific agreement with the doctor treating you.

Read our full colonoscopy patient guide if you want to know more about the procedure itself, or the guide to removal of bowel polyps.