What are the risks of having a colonoscopy?

Colonoscopies can have complications from the bowel preparation, the anaesthetic or the procedures itself. The bowel preparation can make you dehydrated, and the elderly or those with kidney disease are at particular risk. Often I will advise such people have their prep in hospital, where they can have a drip afterward to keep you hydrated. The anaesthetic is usually a sedation rather than a full general anaesthetic, and serious problems are exceedingly uncommon. I quote a 2 in 1000 chance of a serious complication from the colonoscopy itself (although the risk is probably even lower in those younger than 50). That could be either a haemorrahage or a perforation. Both have solutions, but this usually involves hospitalisation and sometimes even need surgery. Remember that 998/1000 don't get this complication.