The C domains of coagulation factors V (FV) and VIII (FVIII) are structurally conserved domains and share a common and essential function in membrane binding. In vivo regulation of thrombin formation strongly depends on the expression and regulation of the cofactor activities of FVIII and FV. With this study, we explored the possibility of inhibition of thrombin formation in full blood with small druglike molecules. Such compounds may serve as lead molecules for the development of a new type of orally available coagulation inhibitors that act by blocking the interaction between the C domains of FVIII and the membrane surface. We identified 9 novel molecules that are able to inhibit binding of the FVIII C2 domain to a model membrane by application of a combined ligand-based and target structure-based virtual screening approach that took into account the knowledge of a set of previously identified low-molecular-weight FVIII binders that were, however, not active in full blood. The half-maximal inhibitory concentration values of our newly identified compounds varied from 2.1 to 19.9 mu M, of which 7 of 9 molecules did not appreciably inhibit FV membrane binding and were thus specific for FVIII. The most active bioactive compound showed activity in both plasma and in full blood.