Efficacy of Flavocoxid 500 mg Compared With Naproxen 500 mg in Subjects With Moderate-severe Osteoarthritis of the Knee

Inclusion Criteria: * Willing and able to read and understand informed consent and questionnaires in English. * Adults of either gender age 35-75 years, in general good health. * Established X-ray diagnosis of osteoarthritis of at least one knee. * Taken NSAID including COX-2 (cyclo-oxygenase-2) inhibitor in full therapeutic dose for at least one month prior to screening. * Able and will to discontinue osteoarthritis medications until flare criteria met. * BMI\</= 45 * Subjects must rate target knee at least 5 out of 10 on discomfort VAS (visual analogue scale) at baseline visit. * Have an increase of at least 15mm on a 100mm pain VAS (visual analogue scale) from screening to baseline visit. * Must use acceptable birth control if female. * Screening fecal occult must be negative. * Able to attend all required visits * Physical Therapy is allowed as long as the type and frequency remains unchanged for the duration of the study. Exclusion Criteria: * Refusal to sign consent. * Inability to attend all clinic visits * Grade 0-1 K-L changes in both knees or grade 4 K-L changes in either knee on standing A/P radiograph * Pregnant or lactating women * History of serious cardio-vascular disease. * Recurrent arrythmias, except paroxysmal tachycardia, cardiomyopathy, myocardial infarct within one year of screening. * History of chronic esophageal, gastric or duodenal disease * History of upper GI bleeding within the past 2 years. * Any GI disorder associated with malabsorption * Any musculo-skeletal or neurological condition that results in pain or gait disturbance that might confound evaluation of target knee. * Uncontrolled Diabetes Mellitus * History of bleeding disorder or concurrent use of coumadin or any agent used to reduce blood clotting or platelet adhesiveness. * Concurrent use of any anti-arthritic medication, including corticosteroids regardless of the reason for use. (low dose aspirin for cardioprotection is allowed) * History of chronic renal disease with creatinine \>2.0 or nephrotic syndrome with 24 hour protein excretion \>1000mg. * Intra-articular injection of any hyaluronic acid preparation in the target knee joint within 4 months of baseline visit. * Intra-articular injection of a corticosteroid in the target knee joint within 2 months of the baseline visit. * BMI\>45 * History of allergic reaction to flavonoid or flavan containing foods or products (example: red wine, colored fruits and vegetable, brazil nuts, tea, natto) * History of allergy to aspirin, naproxen or other NSAID * History of substance abuse including alcohol, or any psychiatric condition that may impair the subject's ability to comply with the study requirements. * Any medical condition that, in the opinion of the investigator, might put the subject at undue risk or might interfere with the subject's ability to participate in the study. * Participation in another clinical trial within 30 days or 7 half lives of the study agent, whichever is longer, of the screening visit.