Cyclooxygenase-1 (COX-1) is a constitutively expressed isozyme of cyclooxygenase that produces prostaglandins important in homeostatic functions of virtually all cells. Among the functions of prostaglandins produced by COX-1 are: maintenance of gastric mucosa, regulation of sleep cycles, control of vascular tone, and control of platelet function. Cyclooxygenase-1 is inhibited by the non-selective non-steroidal antiinflammatory drugs (e.g. ibuprofen, but not rofecoxib).