Heparin is used to prevent blood clots from forming in people who have certain medical conditions or who are undergoing certain medical procedures that increase the chance that clots will form. Heparin is also used to stop the growth of clots that have already formed in the blood vessels, but it cannot be used to decrease the size of clots that have already formed. Heparin is also used in small amounts to prevent blood clots from forming in catheters (small plastic tubes through which medication can be administered or blood drawn) that are left in veins over a period of time. Heparin is in a class of medications called anticoagulants ('blood thinners'). It works by decreasing the clotting ability of the blood.

Warfarin is used to prevent blood clots from forming or growing larger in your blood and blood vessels. It is prescribed for people with certain types of irregular heartbeat, people with prosthetic (replacement or mechanical) heart valves, and people who have suffered a heart attack. Warfarin is also used to treat or prevent venous thrombosis (swelling and blood clot in a vein) and pulmonary embolism (a blood clot in the lung). Warfarin is in a class of medications called anticoagulants ('blood thinners'). It works by decreasing the clotting ability of the blood.

Prescription aspirin is used to relieve the symptoms of rheumatoid arthritis (arthritis caused by swelling of the lining of the joints), osteoarthritis (arthritis caused by breakdown of the lining of the joints), systemic lupus erythematosus (condition in which the immune system attacks the joints and organs and causes pain and swelling) and certain other rheumatologic conditions (conditions in which the immune system attacks parts of the body). Nonprescription aspirin is used to reduce fever and to relieve mild to moderate pain from headaches, menstrual periods, arthritis, colds, toothaches, and muscle aches. Nonprescription aspirin is also used to prevent heart attacks in people who have had a heart attack in the past or who have angina (chest pain that occurs when the heart does not get enough oxygen). Nonprescription aspirin is also used to reduce the risk of death in people who are experiencing or who have recently experienced a heart attack. Nonprescription aspirin is also used to prevent ischemic strokes (strokes that occur when a blood clot blocks the flow of blood to the brain) or mini-strokes (strokes that occur when the flow of blood to the brain is blocked for a short time) in people who have had this type of stroke or mini-stroke in the past. Aspirin will not prevent hemorrhagic strokes (strokes caused by bleeding in the brain). Aspirin is in a group of medications called salicylates. It works by stopping the production of certain natural substances that cause fever, pain, swelling, and blood clots. Aspirin is also available in combination with other medications such as antacids, pain relievers, and cough and cold medications. This monograph only includes information about the use of aspirin alone. If you are taking a combination product, read the information on the package or prescription label or ask your doctor or pharmacist for more information.

Clopidogrel is used to prevent strokes and heart attacks in patients at risk for these problems. Clopidogrel is in a class of medications called antiplatelet drugs. It works by helping to prevent harmful blood clots that may cause heart attacks or strokes.

Ticlopidine is used to reduce the risk of stroke in people who have had a stroke or have had warning signs of a stroke and who cannot be treated with aspirin. Ticlopidine is also used along with aspirin to prevent blood clots from forming in coronary stents (metal tubes surgically placed in clogged blood vessels to improve blood flow). It works by preventing platelets (a type of blood cell) from collecting and forming clots.