Antiplatelets are medications that inhibit the activity of platelets, which help the blood clot after injury. Antiplatelets are used to avoid situations where the blood can clot excessively, potentially causing a heart attack or stroke.

Under normal circumstances, platelets play a crucial role in blood coagulation, clotting and hemostasis (stoppage of bleeding). When a small blood vessel is injured, platelets begin to stick to each other (platelet aggregation). They also adhere to the sides of the injured tissue to form a plug, which becomes covered with strands of thread-like fibrin. Soon the blood clot (plug) shrinks into place and blocks any further loss of blood. Platelets also release chemicals that begin the healing process. Without this important clotting function of the platelets, excessive and potentially life-threatening amounts of blood would be lost after simple cuts or scrapes.

While this process is essential to healing, the activity of platelets can be dangerous in some situations. If a blood clot is formed inside a blood vessel, often as a response to injury to the vessel such as occurs with atherosclerosis, it raises the risk of heart attack or stroke. This may occur when a blood clot grows large enough to block a blood vessel (thrombus), or a piece of clot breaks off, travels through the bloodstream and blocks a blood vessel in another part of the body (embolism).

To help prevent this, physicians may prescribe antiplatelets in patients who are at high risk for developing a thrombus within their blood vessels. Antiplatelets are types of anticoagulants – medications used to help prevent the formation of blood clots when no injury has occurred. They work by reducing the platelets’ stickiness (viscosity). The most common antiplatelet in use today is the over-the-counter drug aspirin, which has been found to prevent platelet binding and clot formation. Today, many physicians place their heart patients on a small daily dose of aspirin (generally 81 milligrams) to prevent the formation of blood clots that may injure the heart. For patients who do not respond to aspirin as a preventive therapy, other antiplatelet medications are available. The most common are clopidogrel and ticlopidine.

Aspirin is an analgesic (pain reliever) that has anti-clotting properties that benefit the heart. However, many other over-the-counter pain relievers do not have the anti–clotting properties of aspirin. These drugs cannot be used as an aspirin substitute to prevent clot-related heart problems. Studies suggest that more than 20 percent of people taking an analgesic for heart disease prevention are taking non-aspirin medications that actually provide no anti-clotting or cardiovascular benefit.

Patients should never take aspirin or any other antiplatelet drug as a preventive measure unless advised to do so by a physician. In addition, antiplatelets should not be taken with anticoagulants unless directed by a physician. While antiplatelets are a valuable preventive tool when used properly, they can cause serious bleeding in some people, and their activity may be affected by a wide range of other medications and substances. Therefore, a physician always needs to carefully review a patient’s condition and medical history before prescribing antiplatelet therapy. In general, patients with a history of internal bleeding (most often gastrointestinal) should not take aspirin.

Types of antiplatelets include: