Research suggested most of the adverse effects of NSAIDs to be mediated by blocking the COX1 (constitutive) enzyme, with the analgesic effects being mediated by the COX2 (inducible) enzyme. Thus, the COX2 inhibitors were developed to inhibit only the COX2 enzyme (traditional NSAIDs block both versions in general).
Research suggests that most adverse effects of NSAIDs are caused by blocking the constitutive COX1 enzyme, while their analgesic effects are mediated by the inducible COX2 enzyme. This led to the development of COX2 inhibitors, which specifically target only the COX2 enzyme (traditional NSAIDs generally block both versions).