O-ASHA is an irreversible, non-selective inhibitor of COX-1 and COX-2. Aspirin is the best-studied example of an irreversible COX inhibitor, acting via the acetylation of the active site serine residue 529 in human COX-1. O-ASHA inhibits ovine COX-1 in a time-dependent, irreversible manner with a 50% B/B0 value of approximately 4.5 mM.{9607}