Anticoagulants prevent pathologic thrombus formation by targeting specific factors in the coagulation cascade. Warfarin inhibits vitamin K epoxide reductase (VKORC1), blocking the gamma-carboxylation of clotting factors II, VII, IX, and X, as well as proteins C and S. Because it affects multiple factors with different half-lives, warfarin has a delayed onset (3-5 days for full anticoagulant effect) and requires bridging with heparin or LMWH for acute thromboembolism. Direct oral anticoagulants (DOACs) target single specific factors: rivaroxaban, apixaban, and edoxaban are direct factor Xa inhibitors, while dabigatran is a direct thrombin (factor IIa) inhibitor. DOACs have rapid onset (1-4 hours), predictable pharmacokinetics, fewer drug-food interactions, and do not require routine laboratory monitoring—making them preferred over warfarin for most non-valvular atrial fibrillation and VTE indications. However, warfarin remains the standard for mechanical heart valves, antiphospholipid syndrome, and severe CKD (CrCl <15-25 mL/min depending on agent). The choice between agents depends on indication, renal function, drug interactions, patient compliance, cost, and reversal agent availability.