Until the 1970s, aspirin was mainly used as an analgesic (pain killer), but today, it is considered one of the most important drugs in treating and preventing cardiovascular diseases. Aspirin lowers the production of prostaglandins, substances that affect various functions of vital organs and tissues. Among other effects, prostaglandins make the platelets aggregate together and form a blood clot. This is obviously very useful in injury to stop bleeding, but blood clots are also responsible for heart attacks and strokes by obstructing arteries and blocking the blood supply to a part of the heart muscle or brain. Aspirin reduces the production of prostaglandins and therefore inhibits excessive clotting and subsequently reduces the risk of heart attack and ischaemic stroke.

Aspirin can cause damage to the mucosa (the lining of the stomach and guts), ranging from mild irritation and dyspepsia up to ulceration with significant bleeding. The risk with 75mg daily in cardiovascular prevention is much lower than in 500-1000mg used previously for analgesia. If needed, drugs called proton pump inhibitors (PPI) such as omeprazole (Losec), lansoprazole (Zoton) or pantoprazole (Pantoloc, Protium) are used to protect the mucosa of the gastrointestinal tract. In case of intolerance or allergy to aspirin, a good alternative is clopidogrel (Plavix).

The benefit of aspirin has been well established in secondary prevention, i.e. in patients who already have coronary artery disease, peripheral vascular disease or a history of ischaemic stroke. However, until recently efficacy and safety of aspirin in primary prevention have been controversial. Specifically, it was unknown whether aspirin could prevent a first cardiovascular event in high-risk patients with diabetes or a combination of cardiac risk factors. The studies ASCEND and ARRIVE, presented at the European Society of Cardiology Congress 2018 in Munich, clarified the issue: There is no net cardiovascular benefit of aspirin in primary prevention. The use of aspirin slightly reduced cardiovascular events, but the increased risk of bleeding offset the benefit. Therefore, the routine use of aspirin in primary prevention, including in patients with diabetes, is not recommended.