PTGS2 and arthritic joint disease: Mamdani did an observational cohort study over a period of 1 year to compare the rates of upper gastrointestinal hemorrhage in patients treated for arthritis with either cox-2 inhibitors or NSAIDs and concluded that there is a lower short term risk of upper gastrointestinal hemorrhage for selective cox-2 inhibitors compared with non-selective NSAIDs.