aspirin

Aspirin is one of the oldest and most-studied drugs in medicine, and in the heart it plays a very specific role: it keeps platelets from clumping. A small daily dose makes the blood slightly less prone to forming the kind of clot that triggers a heart attack on a cracked artery plaque.

It works by permanently disabling an enzyme in platelets called cyclooxygenase-1, which platelets need to make thromboxane A2, a powerful clumping signal. Because platelets cannot repair this enzyme, the effect lasts the platelet's whole lifespan of about a week, which is why low-dose aspirin can be taken just once a day.

Aspirin clearly helps people who already have cardiovascular disease — after a heart attack, with known coronary artery disease, or after certain stents — a use called secondary prevention. In healthy people without known disease (primary prevention), the modest clot benefit is often offset by bleeding, so routine use there is no longer broadly recommended and is decided case by case.

The main downside is bleeding, particularly from the stomach lining, since aspirin also irritates it. Honest counseling weighs a person's clotting risk against their bleeding risk rather than assuming aspirin is harmless because it is sold over the counter.