Haemostasis is a set of processes with the aim to maintain blood in the liquid state in the vascular bed, and in the case of damage to the vessel – to prevent extravasation by clot formation (initially a platelet clot and then a fibrin clot). The main components of haemostasis include: platelets, vessel wall, plasma coagulation system, endogenous inhibitors of coagulation and fibrinolytic system. The stream of blood is also an important factor. Haemostasis is divided into two main phases: coagulation and fibrinolysis. These two phases take place simultaneously and remain in equilibrium. The prevalence of any of these processes is the result of the advantage of enzyme complex activity over the complex of the other process. In everyday practice, every physician encounters drugs that affect haemostasis. At the end of the article, the most commonly used anticoagulants and antiplatelet agents available in Poland are described with the mechanisms of their action. The effect of oral anticoagulants results from the inhibition of the transformation of vitamin K₁ which is essential for the production of coagulation factors II, VII, IX and X. Acenocoumarol and warfarin are currently available in Poland. The group of new oral anticoagulants includes direct inhibitors of activated factor X: rivaroxaban, apixaban and dabigatran – a potent, competitive and reversible direct thrombin inhibitor. Anticoagulants which are used parenterally include unfractionated heparin, low molecular weight heparins and fondaparinux. Antiplatelet drugs can be divided into two groups based on the mechanism of action – drugs acting through the metabolism of arachidonic acid (aspirin) and acting on the platelet membrane receptors (ticlopidine, clopidogrel and prasugrel).