Illustration of components of blood.

M illions of Americans take anticoagulants, or blood thinners, daily to help keep poten­tially dangerous blood clots from forming and to prevent a heart attack or stroke.

These prescription drugs, sometimes used to dissolve existing clots before they cause harm, can be very effec­tive. For the 9 percent of older adults with the heart-rhythm disorder atrial fibril­la­tion (Afib), the meds can reduce the risk of a stroke by up to 70 percent.

For years, warfarin (Coumadin and ­generic), known as a vitamin K antagonist, or VKA, was the drug most commonly used to keep blood flowing smoothly.

Because it carries a risk of severe—even deadly—brain bleeds, users needed blood tests at least weekly at first, then at least monthly. They also had to be careful about certain foods, including those that contain vitamin K—like leafy greens such as kale and spinach—which can inter­fere with blood thinning.

More on Cardiovascular Health

But 2019 guidelines recommend newer blood thinners known as non-vitamin K oral anticoagulants (NOACs) or direct-acting oral anticoagulants (DOACs), such as apixaban (Eliquis), dabigatran (Pradaxa), and rivaroxaban (Xarelto), for most people with Afib. Those guidelines are from the American College of Cardiology, the American Heart Association, and the Heart Rhythm Society. (People with mechanical heart valves and moderate to severe mitral-valve narrowing should still use warfarin.)

These drugs, introduced in the past decade, are as effective as warfarin and less potentially risky, says Peter Noseworthy, M.D., a cardiologist at the Mayo Clinic in Rochester, Minn.

A new French study, published in the Annals of Family Medicine, on 1,866 adults followed for one year, found that those who used VKAs had nearly twice the risk of death from any cause as those who used DOACs. The researchers don’t discuss why the death rate appears to be so much higher in VKA users but note that the finding lines up with earlier analyses from insurance data. 

A 2017 study published in the journal Stroke found that people taking a newer blood thinner were about 50 percent less likely to have a brain bleed than those taking warfarin. And the newer drugs don’t require dietary changes or frequent blood tests.

But they can still increase the risk of bleeding and can affect kidney and liver function, so your doctor will need to check for these at least twice yearly. In the new Annals of Internal Medicine study, the people taking VKAs and those taking DOACs had pretty similar rates of serious events like blood clots and major bleeding, while the VKA group had lower incidences of minor bleeding.

And because older adults with Afib are likely to need a blood thinner for life, it’s essen­tial to take it properly.

Which Blood Thinner Is Best for You?

“It’s hard to say one is better or worse, ­because there isn’t that much data comparing them to one another—we’ve mainly compared them against warfarin,” says Jonathan Halperin, M.D., a professor of cardiology at the Icahn School of Medicine at Mount Sinai in New York City.

But there are differences you may want to ask your doctor about. For instance, apixaban was associated with the lowest risk of major bleeding in a 2016 study published in the journal Chest, and the lowest risk of gastrointestinal bleeding in elderly adults compared with dabigatran and rivaroxaban in a study published in the journal Gastroenterology in 2017.

Dabigatran carries an approximately 10 percent risk of heartburn so severe that patients have to switch drugs, Noseworthy says. And it can’t be crushed, a problem if you have difficulty taking pills.

Take These 4 Smart Steps

If you’re taking a blood thinner, it’s smart to do the following:

Know your dosage. The newer blood thinners come in a standard dosage and a lower one for people with kidney problems, so make sure you’re taking the proper one (and that your doctor has ruled out kidney disease if you’re on the higher one). About 16 percent of patients got the wrong dosage, according to a study published in 2017 in the Journal of the American College of Cardiology.

Time it right. Take it at the same time each day; effects wear off rapidly. Ask your doctor what you should do if you miss a dose. Instruc­tions may depend on which blood thinner you use.

Report side effects. The newer drugs can cause serious, even fatal, bleeding. (The risk of GI bleeding is slightly higher than with warfarin.) Tell your doctor if you also take an antidepressant such as paroxetine (Paxil and generic) or sertraline (Zoloft and generic), which can hike bleeding risks further. (Don’t take aspirin or ibuprofen unless your doctor instructs you to do so.)

Be wise about activity. Get your doctor’s okay before engaging in hobbies in which you could be injured (think motorcycle riding), Noseworthy says.

Contact sports, such as soccer, are a no-go, but you may be able to do activities like skiing and cycling if you wear protective gear. If you get into an accident that causes significant bleeding or you need emergency surgery, you can be given a medication such as idarucizumab (Praxbind) in the emergency room, which will help your blood to clot normally almost immediately.

For those on warfarin, that drug’s effects can be reversed within about an hour with the use of fresh, frozen plasma.

Editor’s Note: A version of this article also appeared in the April 2018 issue of Consumer Reports On Health.