The purpose of this study is to compare the gastroduodenal ulceration rate, gastrointestinal complication rate and non-steroidal anti-inflammatory drug-associated dyspepsia between lansoprazole, naproxen and celecoxib, taken once daily (QD) or twice daily (BID), in participants with osteoarthritis taking low dose aspirin.

This study was designed to compare the effectiveness of reducing the incidence of gastroduodenal ulcers between lansoprazole 30mg QD + naproxen 500mg BID vs celecoxib 200mg QD in subjects with osteoarthritis taking low dose aspirin. Approximately 100 sites across the U.S. will enroll subjects with normal endoscopic findings and negative H.pylori. The duration of the study will be a maximum of 14 weeks including a screening period of up to 2 weeks and a 12 week treatment period. Gelusil will be provided for dyspepsia symptom rescue.

Inclusion Criteria:

• Must require the chronic use of a non-steroidal anti-inflammatory drug for the treatment of osteoarthritis.
• Must be taking daily aspirin for cardiovascular prophylaxis.
• Clinical Laboratory values within normal limits for this population

Exclusion Criteria:

• History of gastric, duodenal or esophageal surgery except simple oversew of an ulcer.
• Evidence of uncontrolled, clinically significant disease.
• History of cancer within the past 5 years.
• Presence of gastroduodenal ulcers, esophageal ulcer or >= 10 gastroduodenal erosions during the screening endoscopy. Known history of gastroduodenal ulcer or bleeding within the past year. Esophageal stricture requiring dilatation.
• Presence of Barrett's esophagus with dysplastic changes.
• Systemic disease affecting the esophagus or a history of caustic or physiochemical trauma or irradiation to the esophagus.
• Sero-tests positive for H. pylori.
• Evidence of Zollinger-Ellison syndrome, esophageal varices, cholecystitis, or pancreaticobiliary tract disease.
• Requires treatment with an excluded medication such as proton pump inhibitors, histamine H2 receptor antagonists, antacids, corticosteroids, lithium, fluconazole, misoprostol, probenecid, methotrexate, anticoagulants, St. John's wart, dong quai, feverfew, garlic, ginger, horse chestnut, red clover or white willow supplements or bisphosphonates.