Although the therapeutic effects of NSAIDs in OA are well established, chronic use of NSAIDs, including both traditional NSAIDs and selective cyclooxygenase-2 (COX-2) inhibitor, have been associated with increased risk of gastrointestinal (GI) complications, ranging from mild gastritis to serious peptic ulcer bleeding [21,22]. This evidence concerns the gene PTGS2 and gastritis.