Atrial Fibrillation (A-fib) and Blood Thinners

Choosing which anticoagulant is best to manage A-fib depends on stroke risk, bleeding risk, and other factors.
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Most people with atrial fibrillation (commonly called A-fib) end up taking some kind of blood-thinning medication on a regular basis. That's because A-fib can substantially increase the chance of developing a blood clot in the heart; if such a clot gets swept out of the heart and into the brain, it can cause a devastating stroke.

Taking an anticoagulant medication such as warfarin or dabigatran can reduce the chance of stroke by 50 to 70 percent. Aspirin can also be used, although it's less effective in bringing down stroke risk. But these medications also cause increased risk of bleeding (most commonly in the stomach and bowel) and can impose other burdens, such as the need for frequent monitoring.

For these reasons, deciding which blood thinner to use (if any) can be a tricky decision for both doctors and patients to make. Together, doctor and patient need to balance the risk of stroke versus the risk of bleeding.

Here are the key considerations that go into the decision, along with the four main options you'll likely be considering:

Key considerations

  • An individualized assessment of stroke risk (see FAQ: What's my risk of stroke from atrial fibrillation?). People with very low stroke risk can opt to take aspirin or even no stroke-preventing medication. For all other people with atrial fibrillation, experts usually recommend an anticoagulant such as warfarin or dabigatran.

  • Whether the person is at particularly high risk for bleeding caused by anticoagulants (see FAQ: What's my risk of bleeding caused by my blood thinner?). People at very high risk for bleeding may be better off taking aspirin instead of a stronger anticoagulant.

  • Whether the person fears strokes more than major bleeding or vice versa.

  • Individual circumstances, such as insurance coverage of medications, the number of other medications being taken, and the ability to keep up with frequent blood checks and dosing changes (if warfarin is being considered).

4 main blood-thinning options


First approved for anticoagulation in 1954, warfarin (brand name Coumadin) is the most commonly prescribed blood thinner. Warfarin works by blocking the action of vitamin K, which the body's liver uses to make certain clotting factors.

Pros: Inexpensive, well known to medical community, requires just once-daily dosing, and its blood-thinning effect can be reversed in the hospital, if necessary (following a bleeding complication or to prepare for surgery, for example) by giving intravenous Vitamin K.

Cons: Requires frequent monitoring to make sure blood isn't thinned too much or too little. Effect can be affected by a change in consumption of leafy greens (which contain vitamin K). Interacts with many commonly used medications. Some people need to take different doses on different days of the week, which can require extra attention. Warfarin is regularly included on lists of top-ten drugs causing emergency room visits, hospitalizations, and serious medical complications.

Best for: People who are at more than very low stroke risk, who aren't on many other medications, or who need an inexpensive medication and aren't at high bleeding risk.

More blood-thinning options


First approved by the FDA in October 2010, dabigatran works by inhibiting thrombin, a key enzyme required for blood to clot.

Pros: Doesn't require monitoring, has fewer interactions with food and medications than warfarin.

Cons: Expensive if not covered by insurance, twice-daily dosing, no antidote available if bleeding occurs (following a bleeding complication or to prepare for surgery, for example), long-term side effects not yet known.

Best for: People who are at more than very low stroke risk, have insurance coverage for the drug, who aren't at high risk for bleeding, who would find regular monitoring difficult, or who are on many other medications that might interact with warfarin.

Note: A similar medication, rivaroxaban (brand name: Xarelto), was FDA-approved in November of 2011 and requires only once-daily dosing.


A staple of the medicine cabinet for more than 100 years, aspirin reduces stroke risk by interfering with the clumping of platelets (cells in the blood that help form clots).

Pros: Inexpensive, available over the counter; also used to reduce the chance of repeat heart attack.

Cons: Doesn't prevent strokes as well as warfarin or dabigatran can. Can potentially cause major internal bleeding, although it's less likely to do so than stronger anticoagulants.

Best for: Those who are reluctant to be on a stronger anticoagulant, those with very low stroke risk, or those who are at high risk of bleeding from a stronger anticoagulant.

No anticoagulant

Some people with A-fib are at such low risk overall for stroke that the risk of bleeding from daily aspirin or a stronger anticoagulant is much higher than the estimated risk of A-fib-related stroke. For these people, many experts recommend no anticoagulation.

Note: Two additional anticoagulants are often used short-term because their blood-thinning action can be quickly turned off. Heparin is a very short-acting medication that requires continuous infusion and is sometimes used during hospital stays. Enoxaparin is a subcutaneous injection that's usually dosed twice daily and can be used in the outpatient setting prior to a planned surgery or procedure.

The bottom line

All anticoagulation medications for people with A-fib have downsides.

  • For those who are at the lowest level of stroke risk, forgoing anticoagulation is reasonable. There will be a small risk of stroke, but the patient will avoid the increased bleeding risk related to taking daily aspirin or anticoagulants.

  • For those who are older than age 65 or have other risk factors for stroke, anticoagulation with warfarin or dabigatran is generally recommended. Which one to choose will depend on a person's insurance situation and individual preferences regarding monitoring, dosing convenience, and availability of an antidote.

  • For those who are unable or unwilling to take a stronger anticoagulant such as warfarin or dabigatran, aspirin is a viable alternative, although it's much less effective at preventing strokes.

For tips on how to keep your anticoagulation level steady, should you decide on warfarin, see Warfarin: 7 Ways to Keep Blood Levels in a Safe Range.

For safety tips that every person on anticoagulation should know, whether using warfarin or dabigatran, see Atrial Fibrillation (A-fib) and Anticoagulants: 4 Ways to Reduce Your Chance of Bleeding.

Dr. Leslie Kernisan

Leslie Kernisan is a clinical instructor in the University of California, San Francisco, Division of Geriatrics, and maintains a popular blog and podcast at BetterHealthWhileAging. See full bio