Diclofenac sodium is a powerful inhibitor of COX-2 and prostaglandin synthase activities, both of them are involved in Prostaglandin E-2 (PGE-2) production.22 Thickening of the synovium is one process that occurs in joints affected by osteoarthritis. Thickening of the synovium causes joints stiffness. Thickening of the synovium occurs due to excessive growth of synovial cells. In osteoarthritis, stimulation of COX-2 enzyme on cells in the synovium causes excessive growth of these cells. In osteoarthritis, the inhibition of COX-2 enzyme activity by curcumin from turmeric rhizome extract is able to reduce the excessive growth of the synovial cells. The combination of curcumin from turmeric rhizome extract and celecoxib could enhance the ability of celecoxib in inhibiting the excessive growth and increased apoptosis of synovial cells in osteoarthritis.23