[vidarh]

The harm can be from the initial screening too. The lifetime risk for complications from routine colonoscopy is around 1.6%. The lifetime risk of colo-rectal cancer is 4-5%.

So already before investigating the result, there's a very real consideration whether increasing the number of colonoscopies is likely to be a net benefit.

[haldujai]

Colonoscopy is confusing because it is both screening and diagnostic/investigating.

Most if not all of the complication/risk (perforation and major bleeding being the ones of note) is from the polypectomy / biopsy part of the colonoscopy.