Inflammation of the pancreas (pancreatitis) is an uncommon but potentially serious complication of endoscopic retrograde cholangiopancreatography (ERCP), a specialized endoscopic examination of the ducts draining the liver and pancreas. Although many different strategies have been tried and studied in attempts to reduce this risk, few have been shown to make a significant difference. Those that have are either very expensive, difficult to administer, or both. Diclofenac, an anti-inflammatory medication most often used to treat arthritis, has shown potential to decrease the risk of post-ERCP pancreatitis. It can be given after the procedure to patients at most risk for the complication, and has few side effects. This study will randomize people in the study to placebo or active medication, to determine if Diclofenac reduces the incidence of pancreatitis.