Phenylbutazone is a NSAID and efficient reducing cofactor for the peroxidase activity of COX. It enhances hydrogen peroxide inactivation of both COX and PGI synthase.

Niflumic acid is a selective inhibitor of COX-2. The IC₅₀ values are 16 and 0.1 µM for human recombinant COX-1 and -2, respectively. The Ki values are 2 and 0.02 µM for ovine COX-1 and -2, respectively.

A non-selective inhibitor of both COX-1 and COX-2 with extensive epidemiology documenting its effective reduction of human colorectal cancer.