Your body needs a healthy flow of blood to get the oxygen and nutrients it needs. Some medical conditions can affect healthy blood flow, putting you at risk of a heart attack or stroke.\nTo help lower this risk, your doctor might prescribe a medicine that will keep the blood from clotting as easily. These medicines are commonly called blood thinners.\nWhile a blood thinner does not really “thin” your blood, it can lower your risk of a heart attack or stroke by preventing blood clots. If you already have a blood clot, these medicines help to keep it from getting bigger and can help prevent your body from forming new clots.\nThese medicines can also raise your risk of bleeding, so it is important to know when bleeding or bruising is unusual and when to talk with your doctor.\nWhat Is a Blood Clot?\nIf you have a cut or bruise, a blood clot is a good thing. When you damage a blood vessel, small pieces of cells in your blood called platelets stick together to form a clot and send out a signal to draw more platelets to your injury. Once your injury heals, your blood clot usually dissolves on its own.\nClotting is an important function that your body needs to heal itself, but some medical conditions, behaviors, or situations can cause dangerous blood clots to form. This can be life-threatening if a clot moves and blocks blood flow to your brain, heart, or lungs.\nWhen Is a Blood Thinner Used?\nBlood thinners are usually prescribed for people who have conditions that affect healthy blood flow, including:\n\nAtrial fibrillation, a type of irregular heart beat that can cause blood to pool in the top chambers of your heart, which can cause blood clots to form\nCongenital heart defects, or heart problems that you are born with\nDeep vein thrombosis, or a blood clot in a large vein, usually in your leg\nHeart valve surgery\nA history of heart attack or stroke\nA history of blood clots\n\nTypes of Blood Thinner Medication\nThere are two main types of blood thinners.\nAnticoagulants\nAnticoagulants, like warfarin (or the brand name Coumadin\u00ae), slow down the chemical reaction that happens when your blood tries to clot and can also keep clots that have already formed from getting bigger. Some anticoagulants require you to have your blood checked regularly to make sure they are working properly.\nAntiplatelet drugs\nAntiplatelet drugs like aspirin or clopidogrel (or the brand name Plavix\u00ae), keep your platelets from sticking together.\nWhat You Need to Know\nBecause blood thinners affect your blood’s ability to clot, you might bleed easier than usual. To avoid complications, it is very important to take your medicine exactly how your doctor tells you.\nSome other medicines and foods make blood thinners stronger or weaker. Talk to your doctor about all the medicines you take, including over-the-counter drugs, vitamins, and supplements, as well as your diet to make sure that you are not at risk of a bad interaction.\nIn case of an emergency, carry a card in your wallet that lists all the medicines you take. It’s also a good idea to have a medical alert bracelet showing that you take a blood thinner.\nCall your doctor right away if you have any of these symptoms, which may be a sign of major bleeding:\n\nBleeding from your gums or nose that does not stop within a few minutes\nA wound that does not stop bleeding after you apply pressure to it\nBlood in your urine or stool\nStools that are black like tar\nVomiting or coughing up blood\nBruises that appear for no reason, get larger or more painful, or are sudden and severe\n\nTo learn more about blood thinners, visit the UPMC Heart and Vascular Institute online or call 1-855-UPMC-HVI (876-2484).