Most doctors' offices advise against drinking alcohol the night before a colonoscopy because it leads to dehydration, explains Colon & Rectal Surgery Associates. To avoid interactions with the medications administered during the colonoscopy, patients are recommended to avoid alcohol for 24 hours after the procedure, notes MedlinePlus.
Doctors usually prescribe a clear liquid diet and a bowel-cleaning regimen starting the day before the colonoscopy. Some examples of items on a clear liquid diet include black coffee, gelatin, sports drinks, broth and water, states MedlinePlus. Depending on the patient's medical conditions, doctors sometimes advise stopping certain medications before a colonoscopy, including aspirin, ibuprofen, iron pills and blood thinners.