Thrombin is a "trypsin-like" serine protease that is encoded by the F2 gene in humans. Thrombin is produced by the enzymatic cleavage of two sites on prothrombin by activated Factor X (Xa). Thrombin in turn acts as a serine protease that converts soluble fibrinogen into insoluble strands of fibrin. Thrombin is also active in the catalysis of many other coagulation-related reactions.

Thrombin is implicated as a major factor in vasospasm following subarachnoid hemorrhage. Blood from a ruptured cerebral aneurysm clot around a cerebral artery, releasing thrombin. This can induce an acute and prolonged narrowing of the blood vessel, potentially resulting in cerebral ischemia and infarction (stroke). Beyond its key role in the dynamic process of thrombus formation, thrombin has a pronounced pro-inflammatory character, which may influence the onset and progression of atherosclerosis [2][3].