Colonoscopy side effects

Colonoscopy side effects: what is normal and when to react

Colonoscopy is a safe examination, and most patients go home with nothing more than a bit of bloating. Still, it is good to know what is normal after an endoscopic examination of the colon and which side effects mean you should call the clinic or out-of-hours services. This is the run-through we give at Kirurgen.dk in Charlottenlund.

Common, completely normal effects

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

• abdominal cramping and mild bloating from the air introduced into the bowel
• urge to burp and passing of wind. This settles as soon as the air is 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 are expected. Rest and drink plenty of water.

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. Drinking sugary clear fluids helps to prevent headache and nausea from fluid and electrolyte loss.

Side effects from sedation

If you choose sedation (most often midazolam and fentanyl), you may notice:

• drowsiness and mild dizziness for 4–6 hours
• a transient memory gap around the procedure itself. This is normal and resolves on its own
• mild nausea

You cannot drive a car, ride a bike, operate machinery or sign important documents for the rest of the day.

Rare but serious complications

These affect fewer than 1 in 1,000 colonoscopies, but 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 for hours need to be assessed
• Perforation (a hole in the bowel wall). Very rare but serious. Symptoms are severe persistent abdominal pain, a hard distended abdomen, fever above 38.5°C, chills
• 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 the clinic during opening hours on +45 39 64 01 25, or 1813 (out-of-hours GP) or 112 (emergency) outside those hours, if you experience:

• severe or persistent abdominal pain for more than 3 hours
• fever above 38.5°C
• chills
• significant rectal bleeding that does not stop
• breathing difficulty or chest pain
• vomiting that will not stay down

Timeline: what you feel and when

When	What is normal	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	Normal bowel motions return	Fever, chills, abdominal pain
Up to one week	Quiet course	Late-onset pain or bleeding

Fewer side effects next time

Most complications relate to polyp removal and blood-thinning medication. We always review your medication before the procedure and give clear advice on which tablets to pause and when to restart. Follow the advice carefully and the risk of side effects stays as low as possible.

Read our full colonoscopy patient guide if you want to know more about the procedure itself.