Celecoxib, the generic of Celebrex, is a Non-Steroidal Anti-Inflammatory Drug (NSAID) used to treat chronic joint pain, such as arthritis or pain caused by local swelling. Like all NSAIDs, celecoxib blocks the production of prostaglandins, which are hormones that are released in affected areas (i.e., joints) and cause swelling and increased sensitivity.
Since not all prostaglandins do the same thing, celecoxib is tailor made to target just the prostaglandins that cause local swelling (cox-2) and not the ones that help protect our GI tract (cox-1). Essentially, celecoxib is a pain relief drug that is safe to use for extended periods without having to worry about undue damage to the stomach lining.
Since celecoxib is a drug intended for use in humans, its use in dogs or cats is considered an extra-label drug, and should not be given without a prescription from a vet.