FDA Approves a New Type of Clot Blocker to Help Prevent a Second Stroke

The U.S. Food and Drug Administration has approved the first drug it has cleared that blocks factor XIa, a protein the body uses to build clots, for adults at high risk of a second stroke. The agency cleared Sunharbo (asundexian) on Nov. 9, 2026, for people who have recently had a mild-to-moderate stroke caused by a clot that did not come from the heart. It also covers a high-risk transient ischemic attack, often called a mini-stroke.

The drug is a tablet taken once a day on top of antiplatelet drugs, which keep platelets from clumping. Hylton V. Joffe, who directs the FDA office that reviews heart and blood drugs, said stroke is a leading cause of disability and death in the United States and that survivors are at risk of having another one. "Today's approval represents a meaningful advance for patients and health care providers seeking a new option for secondary stroke prevention," he said.

In its announcement, the FDA says the approval rests on OCEANIC-STROKE, a phase 3 trial of 12,327 adults. Participants were assigned at random to the drug or a placebo within 72 hours of their symptoms starting, and both groups also took antiplatelet drugs. Over a median of 14.2 months, the drug lowered the risk of ischemic stroke by 26% compared with placebo.

On bleeding, the FDA reports that overall major bleeding was similar in the two groups. It was higher with Sunharbo among patients older than 75 and during the first 90 days of treatment, and bleeding in the gut was more common than with placebo. Diarrhea was the side effect reported most often.

The FDA says the drug is not approved for preventing stroke in people with atrial fibrillation, an irregular heart rhythm. It is also not recommended for patients with moderate or severe liver impairment, or alongside medicines such as the anti-seizure drug carbamazepine, which can make it less effective. The agency gave Sunharbo Fast Track and Priority Review designations, and granted the approval to Bayer HealthCare Pharmaceuticals.