This chapter presents a comprehensive review of pharmacological agents that act on blood, with a focus on their clinical relevance in anaesthesia and critical care. The chapter begins by examining the properties, indications, and transfusion considerations of blood products, including red blood cells, platelets, plasma, and coagulation factor concentrates. It then explores anticoagulant drugs, detailing their mechanisms of action, pharmacokinetics, clinical indications, and management strategies, including reversal agents and perioperative considerations. Both traditional anticoagulants, such as heparins and vitamin K antagonists, and direct oral anticoagulants (DOACs) are discussed extensively. The chapter also covers antiplatelet agents, including aspirin, P2Y₁₂ inhibitors, and glycoprotein IIb/IIIa inhibitors, highlighting their clinical applications and implications for perioperative bleeding risk and management. Special attention is given to drug interactions, monitoring requirements, and patient safety in high-risk settings. By integrating foundational pharmacology with practical clinical strategies, this chapter equips trainees to effectively manage haemostasis and thrombosis in perioperative and critical care environments.