FDA Approves Sunharbo, the First Factor XIa Blood Thinner to Prevent Repeat Strokes
The U.S. Food and Drug Administration on Monday approved Sunharbo, the first medicine in a new class of blood thinners designed to prevent a second stroke, giving doctors a new option for patients who have just survived a stroke or a so-called mini-stroke.
The drug, known by its generic name asundexian and made by Bayer, is a once-daily 50-milligram tablet taken alongside standard antiplatelet therapy. It is the first factor XIa inhibitor ever approved in the United States, and the approval rests on a 12,327-patient global trial that found it cut the risk of another ischemic stroke by 26 percent without a significant rise in major bleeding.
What Sunharbo Is and Who Can Take It
Sunharbo is approved for adults who have had a recent mild-to-moderate non-cardioembolic ischemic stroke — a stroke caused by a clot that did not originate in the heart — or a high-risk transient ischemic attack, often called a mini-stroke. Patients in the trial had a National Institutes of Health Stroke Scale score of 15 or less, meaning their stroke was mild to moderate.
The drug works by blocking factor XIa, a protein in the blood-clotting cascade. The idea behind the new class is to interrupt clot formation enough to prevent strokes while interfering less with the body’s normal ability to stop bleeding than older anticoagulants do. That balance has been the central promise of factor XIa research for years, and Sunharbo is the first drug in the class to reach American patients.
It is taken as one 50-milligram tablet a day, in addition to antiplatelet therapy such as aspirin or clopidogrel, not instead of it. The FDA granted the drug both Fast Track and Priority Review designations, and the approval was granted to Bayer HealthCare Pharmaceuticals Inc. of Whippany, New Jersey.
What the OCEANIC-STROKE Trial Showed
The approval was based on OCEANIC-STROKE, a phase 3, randomized, double-blind, placebo-controlled trial conducted at 702 centers in 37 countries and published in the New England Journal of Medicine in April 2026. Participants were enrolled within 72 hours of their stroke or mini-stroke and randomly assigned to asundexian or a placebo, with both groups also receiving antiplatelet therapy. The average patient was 68 years old, and about one-third of participants were women.
Over a median treatment period of 14.2 months, recurrent ischemic stroke occurred in 6.2 percent of patients taking asundexian, compared with 8.4 percent of those on placebo — a 26 percent relative reduction, with a hazard ratio of 0.74 and a 95 percent confidence interval of 0.65 to 0.84. In absolute terms, the drug prevented about two recurrent strokes for every 100 patients treated.
Crucially for a blood thinner, the overall rate of major bleeding was similar in the two groups, at 1.6 events per 100 patient-years with asundexian versus 1.5 with placebo. The trial’s lead investigator, Dr. Mike Sharma of Hamilton Health Sciences in Canada, has said the results give doctors a new way to protect patients in the weeks and months after a stroke, when the risk of another one is highest.
Not every measure favored the drug. A secondary outcome looking at stroke risk within the first 90 days missed statistical significance, with a hazard ratio of 0.84 and a confidence interval stretching from 0.69 to 1.02 — a reminder, researchers note, that the class’s promise is not yet fully proven.
The Bleeding Question
The FDA’s announcement was careful about safety. While major bleeding overall was similar between the groups, bleeding was increased with Sunharbo in patients older than 75 and during the first 90 days of treatment. Gastrointestinal bleeding occurred more commonly with the drug than with placebo, and the most frequently reported side effect was diarrhea, affecting at least 3 percent of treated patients.
The label carries several practical warnings. Sunharbo is not recommended together with medicines that are combined P-gp and strong CYP3A4 inducers, such as the seizure drug carbamazepine, because they can reduce its effectiveness. It is not recommended for patients with moderate or severe liver impairment. Patients should stop taking it at least 24 hours before elective surgery or invasive procedures, and for at least 24 hours after receiving clot-busting treatment for an acute stroke.
What Sunharbo Is Not Approved For
The approval is deliberately narrow. Sunharbo is not approved to prevent strokes in people with atrial fibrillation, the irregular heartbeat that is one of the largest markets for blood thinners. That distinction matters: patients with atrial fibrillation need full anticoagulation, and Sunharbo is not a substitute for it.
The drug is also not a treatment for an acute stroke in progress. It is a prevention medicine for people who have already had a stroke or a high-risk mini-stroke and are trying to avoid another one.
Price and Availability
Bayer said it expects to begin shipping Sunharbo this month, with hospitals and pharmacies able to order it soon after. The company set a list price of $748.50 for a 30-day supply, a figure that experts say could slow initial uptake until insurers decide on coverage.
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Asundexian was approved in China last month and is currently under review by regulators in Europe and Japan. Bayer is also running a post-approval registry to gather more evidence on how the drug performs in routine practice, including in patients who were underrepresented in the trial.
Why This Matters
Stroke is a leading cause of disability and death in the United States, and survivors live with a persistent fear of a second one. About 5 percent of people who have an ischemic stroke or a mini-stroke have another within a year, and roughly one in five who survive a minor stroke or mini-stroke is dead or disabled within five years. Existing prevention relies mainly on antiplatelet drugs, which leave a substantial residual risk.
“Stroke is a leading cause of disability and death in the United States, and survivors are at risk of having another stroke,” said Dr. Hylton V. Joffe, director of the FDA’s Office of Cardiology, Hematology, Endocrinology, and Nephrology. “Today’s approval represents a meaningful advance for patients and health care providers seeking a new option for secondary stroke prevention.”
The approval also matters beyond stroke. Factor XIa inhibitors have been one of the most closely watched ideas in cardiovascular medicine for a decade, and Sunharbo’s success — or failure — in the real world will shape whether the class expands into other uses, including prevention after heart attacks and in other clotting disorders.
The news comes in a busy stretch for the FDA. Just a day earlier, the FDA ordered a class-wide vision-loss warning on GLP-1 weight-loss drugs, and Eli Lilly’s Foundayo pill cut sleep apnea episodes by up to 44 percent in a late-stage trial. Meanwhile, newborn bleeding cases nearly doubled in 2025 as more parents declined the vitamin K shot, a reminder that prevention stories cut both ways.
What Happens Next
Doctors and patient groups will now watch how quickly insurers cover the drug and how it performs outside the controlled conditions of a trial. The first real-world test will be whether the bleeding profile seen in OCEANIC-STROKE holds up in older and sicker patients, the group most at risk of both stroke and bleeding.
Bayer’s post-approval registry is expected to provide some of those answers, and regulators in Europe and Japan are weighing their own decisions. For now, the approval gives stroke survivors and their doctors something they have not had before: a new kind of blood thinner, built on a different part of the clotting system, with trial evidence that it prevents repeat strokes without a major increase in serious bleeding.
Frequently Asked Questions
What is Sunharbo?
Sunharbo is the brand name for asundexian, a once-daily tablet made by Bayer. It is the first factor XIa inhibitor approved by the FDA, a new class of blood thinner that blocks a protein involved in clot formation. It is taken together with antiplatelet therapy to reduce the risk of another stroke after a recent stroke or mini-stroke.
Who can take Sunharbo?
Adults who have had a recent mild-to-moderate non-cardioembolic ischemic stroke or a high-risk transient ischemic attack (mini-stroke). It is not approved for stroke prevention in people with atrial fibrillation, and it is not recommended for people with moderate or severe liver impairment.
How well does it work?
In the 12,327-patient OCEANIC-STROKE trial, Sunharbo cut the risk of a repeat ischemic stroke by 26 percent compared with placebo — 6.2 percent of treated patients had another stroke versus 8.4 percent on placebo. Major bleeding rates were similar overall, though bleeding was higher in patients over 75 and in the first 90 days of treatment.
How much does Sunharbo cost?
Bayer set a list price of $748.50 for a 30-day supply. Actual out-of-pocket costs will depend on insurance coverage, which is still being decided. Bayer expects to start shipping the drug in November 2026.
Stroke survivors have long had only a handful of tools to prevent a second stroke. Sunharbo does not replace them, but for the first time, it adds a genuinely new one — a drug that targets a different step in clotting, backed by a large international trial and a narrow, clearly defined approval. Whether it becomes a routine part of stroke care will depend on what happens next: coverage decisions, real-world safety data, and the judgment of the doctors who prescribe it.
Sources: U.S. Food and Drug Administration, “FDA Approves First Factor XIa Inhibitor to Help Prevent Stroke in Certain Adults at High Risk,” Nov. 9, 2026; Sharma M, Dong Q, Hirano T, et al., “Asundexian for Secondary Stroke Prevention,” New England Journal of Medicine 2026;394(15):1467-1479; STAT; AJMC; NeurologyLive; TCTMD; Pharmacy Times.
