Your doctor will decide which group you're in. The two most common blood thinners are called heparin and warfarin. Your doctor will probably give you heparin first, because heparin works right away. Heparin must be injected with a small needle under the skin. Once the heparin starts working, your doctor will probably have you start taking oral warfarin.
Warfarin takes longer to begin working.
Both medicines can cause you to bleed more easily. You might notice that, if you cut yourself, the blood takes longer to clot. You might bruise more easily. If you have any unusual or heavy bleeding, call your doctor. Warfarin has a stronger effect on some people than on others.