Can colonoscopy prep make you sick?

Possibly: The prep called GoLytly is polyethelyne glycol which when ingested causes an outpouring of body fluid into the GI tract which can lead to dehydration. It is more important to have a bland diet without roughage several days before and use a Fleet enema (sodium bisphosphate) to clean the distal colon. A clean colon is the important issue and not the total use of oral meds to clean out the bowel.