Larry Bordeaux, 65, has been on blood thinners since 2010, after he started developing deadly clots following an operation.
He credits the drugs with saving his life. If he stops taking them for several days — which he must sometimes do before certain medical procedures — clots develop quickly.
Still, Bordeaux, of Havelock, North Carolina, knows that being on blood thinners is a double-edged sword: They put him at a heightened risk of serious, uncontrolled bleeding. Since he started taking them, Bordeaux has experienced complications ranging from a serious hematoma — in which a pool of blood forms outside of blood vessels — to gastrointestinal bleeding.
“Even with something like a simple fall, if the blood thinner [dose] is not correct, I could bleed out,” said Bordeaux, who has since become involved with the National Blood Clot Alliance, a nonprofit organization that aims to reduce deaths and complications from blood clots, as well as prevent adverse events linked to blood thinners.
Bordeaux is just one of more than 8 million people in the U.S. who take blood thinners, also called anticoagulants. Many, like him, are prescribed the drugs after they develop clots following surgery. Others take blood thinners because of an age-related heart rhythm disorder called atrial fibrillation, which makes clots likelier to form.
Blood clotting, of course, is an essential process in the body to stop bleeds. But when blood clots form too readily, it can block blood flow, leading to embolisms, heart attacks and stroke. Blood thinners work by interfering with the body’s normal blood clotting process. At the same time, the drugs are also responsible for a staggering number of unintended bleeding events, sending hundreds of thousands of older people to the hospital every year. A study in the American Journal of Medicine estimates that that costs the health care system more than $2.5 billion every year.
“While they prevent stroke and embolism, they do cause bleeding,” said Dr. Samin Sharma, director of the Cardiovascular Clinical Institute at Mount Sinai Fuster Heart Hospital in New York City. “Studies have shown that they decrease the [risk of an] ischemic stroke, but the [risk of a] hemorrhage stroke goes slightly up.” (Ischemic strokes are caused by blockages, while hemorrhagic strokes are caused by bleeds.)
Even President Donald Trump has mentioned the risks linked to blood thinners, in particular aspirin, which he takes daily. “I take the larger one, but I’ve done it for years, and what it does do is it causes bruising,” he told The Wall Street Journal at the end of last year.
According to Dr. Pieter Cohen, an associate professor of medicine at Harvard University, who carried out a recent study on emergency room visits due to blood thinners, the most common issue is bleeding in the stomach or the wider GI tract.
“A bunch of those people need to be hospitalized to stabilize the situation, or they may need a transfusion,” Cohen said. “So that can be very serious. A very swift, massive GI bleed that cannot be stabilized can lead to disability or death.”
People taking anticoagulants can also experience serious bleeds from small cuts or grazes, uncontrolled nosebleeds, blood in the urine and, more rarely, brain hemorrhages or bleeding in the lungs.
“If you have a source of blood loss, anticoagulants increase the likelihood that you will lose more blood, that you will require a transfusion and that you’ll have a worse outcome,” said Arthur Allen, a clinical pharmacist and president-elect of the Anticoagulation Forum, which is working to establish better ways of reducing risk of serious bleeds.
Yet advocates feel that many patients and their families are not sufficiently informed of the risks related to blood thinners.
“Bleeding events aren’t rare edge cases; they happen every day,” said Leslie Lake, president of the National Blood Clot Alliance. “The staggering part is not just the numbers, but how quietly these events occur, often dismissed as complications rather than preventable harms.”
Many of those harms are preventable: Research suggests that almost half of all adverse events related to such drugs could be avoided.
So what can be done better?
A new class of blood thinners
Blood thinner harm was not supposed to still be a major issue. For nearly 60 years, the drug of choice was warfarin, which was originally developed as a rat poison. The major limitation of warfarin is that it does not work uniformly, and patients need regular blood tests to constantly monitor and adjust the dose.
“Warfarin was a very, very tricky drug,” Allen said. “There was a constant balancing act that required getting a blood test done anywhere from once a week to once a month.”
In 2010, a new class of blood thinners arrived, known as direct oral anticoagulants, or DOACs. Four of them are available in the U.S. — apixaban (sold under the brand name Eliquis), dabigatran (brand name Pradaxa), edoxaban (Savaysa) and rivaroxaban (Xarelto) — and clinical trials have shown them to be safer and more consistent than warfarin.
Yet in the real world, that has not translated to improved safety. More than a decade since the new class of blood thinners were introduced, about 300,000 people in the U.S. taking anticoagulants still end up in the emergency department every year with bleeds, and the proportion being hospitalized on the newer drugs remains similar to that of warfarin, according to a 2024 study.
Why? Part of the promise of the newer drugs was that they did not require the same degree of monitoring as warfarin. Because of that, Allen said he is concerned that the new generation of blood thinners is sometimes prescribed without sufficient oversight. In particular, the risk of bleeds can be aggravated when blood thinners are prescribed for too long or through overmedication, with one particularly pertinent example being when blood thinners are given alongside antiplatelet drugs — another class of anti-clotting medications that are commonly prescribed after people have experienced cardiac events.
“There’s a suggestion that a third of patients who are on anticoagulants are also on antiplatelet agents, and often inappropriately,” Allen said. “In reality, antiplatelets are rarely indicated in combination with anticoagulants, and when they are, it’s usually [supposed to be] time-limited.”
In a statement to NBC News, Daiichi Sankyo, which makes Savaysa, said that the drug is used to reduce the risk of stroke and clots but added that anticoagulants can increase the risk of serious bleeding. The statement also noted that patients’ kidney function should be checked before they start treatment.
Johnson & Johnson, which makes Xarelto, said in a statement that the drug reduces risk of clots and stroke for adults with certain medical conditions, but they encourage patients to speak with their health care providers to understand the benefits and risks of any medication. Bristol Myers Squibb and Boehringer Ingelheim, makers of Eliquis and Pradaxa, respectively, did not respond to requests for comment, but both websites mention the risk of bleeding from the drugs.
Another issue is patients taking blood thinners alongside common anti-inflammatories such as aspirin, which also acts as a blood thinner and is also known to increase bleeding risk. A study in Michigan found that 1 in every 3 patients taking blood thinners for atrial fibrillation or venous thromboembolism — a serious condition where clots form in deep veins — were also regularly taking aspirin.
“Aspirin is very readily available over the counter, and if the patient hasn’t been educated enough, that can lead to serious adverse outcomes,” said Dr. Sabine von Preyss-Friedman, a geriatric specialist and president of the Post-Acute and Long-Term Care Medical Association.
Experts say another common and often overlooked limitation of anticoagulants is that even with the newer generation of the drugs, doctors need to take care to prescribe the appropriate drug and dose for a patient. If the original dose is too high or it is not adjusted over time — to account for changes in kidney function, weight and patients’ increased risk of falling as they get older — the risk of serious or fatal bleeding events increases.
Cohen said that in prescribing apixaban, the most commonly used blood thinner in the U.S, the typical dose is 5 milligrams twice daily but that for people over 80, the dose should be half of that.
Weighing the risks
Can more bleeds be prevented? While hematologists and vascular medicine doctors have the most expertise managing blood thinners, the ubiquitous nature of the medications means they are prescribed by everyone from primary care physicians to cardiologists. Allen said dosing errors could be avoided by training more vascular medicine doctors.
Sharma said that when the bleeding risk is deemed too high, it is better not to prescribe such drugs at all.
“Sometimes you have to make a decision,” he said. “If you think there’s a high chance of bleeding and the stroke risk is low to intermediate, we can make a decision that giving anticoagulants will be more risky.”
These are not always easy choices to make, and anticoagulation experts like Allen are wary of creating a world where doctors are too scared to prescribe blood thinners, as that would be likely to lead to more strokes and even more preventable harm.
Instead, some hospitals are turning toward predictive models to help doctors weigh patients’ risk of bleeding versus their risk of stroke.
Toby Trujillo, a professor in the clinical pharmacy department at the University of Colorado Anschutz, said emerging AI tools could help doctors identify the correct dose for a patient, as well as prioritize which patients need to be seen by specialists.
“Some health systems across the country have worked with their electronic health record system to develop what is known as a ‘DOACX Dashboard,’” Trujillo said. “Once it is available, it will flag patients on DOAC therapy that are in need of a specialist. The dashboard may identify patients who may have started on a new medication that interacts with a DOAC, patients who have had a change in their kidney function or who have been prescribed an inappropriate dose. This can help focus the expertise of specialists to patients who need them.”
Newer treatment possibilities are also on the horizon. Experts are studying whether ablation — a surgical procedure that uses either heat or cold energy to create tiny scars in the heart to block the faulty electrical signals driving irregular heartbeats — can be a better long-term solution for atrial fibrillation, allowing patients to stop taking blood thinners.
Clinical trials are looking at a new generation of blood thinners known as Factor XIa inhibitors, which work by targeting a particular protein involved in the clotting process and may have a lower risk of bleeding than the current versions.
“Inhibiting this specific coagulation protein carries the potential for maintaining efficacy in preventing clots, but with a lower risk of bleeding,” Trujillo said. “If they do show a reduced risk of bleeding compared to the DOACs, that will be another advance in making anticoagulation safer.”
Whether it’s newer medications or simply better management, Allen said, finding ways to address patient harm linked to blood thinners could go a long way to prevent adverse events that affect hundreds of thousands of people and their families every year.
Von Preyss-Friedman agreed.
“I think we can really prevent a lot of GI bleeds, traumatic brain injuries and all kinds of emergency department visits if we get this under better control,” she said.