Post-ERCP pancreatitis can be a serious complication to ERCP. Two studies have shown a promising preventive effect of glyceryl nitrate. This study should provide a final answer to the clinical question: Does glyceryl nitrate prevent post-ERCP pancreatitis? The study is a prospective, randomized, double blind, placebo-controlled multicenter trial. The investigators intend to include 1600 patients from Norway, Sweden, Denmark, and France.