A patient takes blood thinners to reduce his risk of stroke or heart attack, explains Medline Plus. He would also take blood thinners if he has had heart valve surgery, suffers from a congenital heart defect or has an arrhythmia. Patients might take blood thinners if they are obese or have phlebitis, according to the Texas Heart Institute. Blood thinners, or anticoagulants, reduce blood clots in a patient's blood vessels.
There are two ways that these drugs prevent blood clots from forming, reports MedlinePlus. Anticoagulants slow down the chemical reactions that lead to the formation of a blood clot. Antiplatelet drugs stop platelets, tiny blood cells involved in tissue repair, from coming together and forming clots.
Some patients take blood thinners in pill form, but more powerful blood thinners, such as heparin, require injection, notes the Texas Heart Institute. Injection of blood thinners usually occurs in the hospital so the staff can monitor the patient for complications.
Many drugs increase or decrease the effectiveness of blood thinners, according to the Texas Heart Institute. Because of this, it is important for the doctor to know the patient's complete medical history and for the patient to tell the doctor of any drugs or supplements he takes regularly before he begins treatment with blood thinners.