Harvard Health Letter

What you should know about: The latest blood thinners

For people who are at risk for blood clots and need an anticoagulant (also called a blood thinner), warfarin (Coumadin) has, until recently, been the only oral drug available. It received FDA approval in 1954. It's not especially expensive, and it's generally effective.

But there are problems with warfarin. Dosing with warfarin is complicated. Blood clots can form if the dose is too low, and bleeding can occur if the dose is too high. "Warfarin accounts for the most emergency hospitalizations in adults over the age of 65 for adverse drug events," says Dr. Sam Goldhaber, a Harvard Medical School professor and an authority on anticoagulation.

So people taking warfarin need frequent blood tests to see if the dose needs to be adjusted. Also, warfarin takes five to seven days to become fully active as an anticoagulant. Finally, it causes other side effects besides bleeding, primarily hair loss, fatigue, and a cold feeling.

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