alleviates breathlessness, reduces anxiety and has favorable action on hemodynamic parameters and cardiac oxygen consumption. However, in patients presenting without ST elevation, morphine has been shown to have adverse events potential, and its use is considered acceptable only after inadequate pain relief by medication specific against angina. Non-steroidal anti-inflammatory drugs are contraindicated for both categories of patients. Antiplatelet drugs All patients with acute coronary syndrome must immediately receive antiplatelet therapy, including aspirin and generally a second oral antiplatelet agent. Bleeding is the most important side-effect of antiplatelets. Aspirin Aspirin inhibits platelet aggregation and formation of blood clots. It is effective across the entire spectrum of acute coronary syndromes, and it actually has been shown to reduce the rate of death in patients with STEMI and in patients presenting without ST elevation. Aspirin is contraindicated in patients with documented allergy or known platelet disorder. Patients who have had gastrointestinal symptoms while on long-term aspirin therapy are usually able to tolerate aspirin in the short term. For patients with true intolerance to aspirin clopidogrel is recommended. Lower doses need days to achieve full antiplatelet effect, therefore a loading dose is necessary for patients who are not already on aspirin. P2Y12 inhibitors Aside from aspirin, three antiplatelet agents taken by mouth have been approved for use in acute coronary syndromes, clopidogrel, ticagrelor and prasugrel; all reduce platelet aggregation by inhibiting the P2Y12 receptor, a type of adenosine phosphate receptor, on the surface of platelets. Not all three of them are equally indicated in all types of acute coronary syndromes. In patients with ST elevation the choice of P2Y12 inhibitor depends on reperfusion strategy; for patients undergoing primary percutaneous coronary intervention ticagrelor and prasugrel are considered superior to clopidogrel, as they are more potent and have more rapid onset of action, at the cost of some increase in bleeding risk; for STEMI patients who are treated with fibrinolysis and those who do not undergo reperfusion treatment only clopidogrel is indicated. Prasugrel must not be given to patients with a history of ischemic stroke or aged 75 years or older. In patients with non-ST elevation acute coronary syndrome current guidelines also recommend immediate administration of dual antiplatelet therapy upon diagnosis; clopidogrel and ticagrelor are indicated in this setting, with ticagrelor considered superior for patients undergoing early invasive strategy (see later). However, emerging evidence questions this strategy. As with aspirin, it is necessary to administer a