 refusal to sign informed consent age 18 years pregnancy lactation allergy to any nonsteroidal antiinflammatory drugs patients that have taken any nonsteroidal antiinflammatory drug in the previous seven days before randomization except acetylsalicylic acid in doses up to 300 mgday patients on antiplatelet or anticoagulation therapy except acetylsalicylic acid in doses up to 300 mgday history of gastric or duodenal ulcer history of GI bleeding or perforation history of or active inflammatory bowel disease severe liver disease defined as presence of history of ascites andor esophageal varices severe kidney disease defined as glomerular filtration rate 30 mlmin history of myocardial infarction or cerebrovascular disease history of peripheral arterial disease congestive heart failure NYHA III-IV history of systemic lupus erythematosus Protocol: Patients referred for colonoscopy during their hospital stay will be informed about the trial protocol and possible risks and adverse events, after which they will be offered to accept to be included in the trial by signing the informed consent form. Upon inclusion, patients will be randomized by computer random number sequence generation to either Group 1 diclophenac or Group 2 placebo. Patient allocation will be withheld from all participants in the trial and stored at a secure central location. 