The United States Food and Drug Administration (FDA) has approved a new medicine aimed at reducing the risk of a second stroke in adults who have recently had one. The drug, Sunharbo, whose active ingredient is asundexian, was approved on 9 November 2026 and is the first medicine in a new class known as factor XIa inhibitors to be cleared by the regulator. It is taken as a 50 mg tablet once a day, alongside standard antiplatelet therapy, by adults who have had a recent mild-to-moderate stroke caused by a blood clot that did not start in the heart, or a high-risk transient ischaemic attack, often called a mini-stroke.

What the trial showed

Approval was based on the OCEANIC-STROKE trial, a large international phase 3 study involving 12,327 adults. Participants were assigned at random to receive either Sunharbo or a placebo within 72 hours of their stroke or mini-stroke, with both groups also receiving antiplatelet treatment. Over a median treatment period of 14.2 months, those taking Sunharbo had a 26 per cent lower risk of ischaemic stroke than those taking the placebo. Researchers followed participants for a median of 19 months and reported that the benefit did not fade over that period.

The result matters because existing antiplatelet treatment has changed little in decades, and earlier attempts to strengthen stroke prevention have often failed through lack of effect or extra bleeding. Doctors involved in the trial said the new approach works on a different part of the clotting process, aiming to reduce harmful clots while having a smaller effect on normal clotting.

Safety and side effects

Overall rates of major bleeding were similar between the two groups. The FDA noted, however, that major bleeding was higher with Sunharbo in people older than 75 and during the first 90 days of treatment. Bleeding in the stomach and gut was also more common with the drug. The most frequently reported side effect was diarrhoea, affecting 3.4 per cent of those on Sunharbo compared with 2.8 per cent of those on placebo. The regulator said the medicine should be stopped at least 24 hours before planned surgery or invasive procedures, and for at least 24 hours after clot-busting treatment for an acute stroke.

Who the drug is for

Sunharbo is intended only for the group studied in the trial: adults with a recent non-cardioembolic ischaemic stroke with a stroke severity score of 15 or less, or a high-risk transient ischaemic attack. It is not approved to prevent stroke in people with atrial fibrillation, and it is not recommended for people with moderate or severe liver impairment. It should also not be combined with medicines that are both P-glycoprotein and strong CYP3A4 inducers, such as carbamazepine, because these can reduce its effectiveness. The FDA gave the application fast-track and priority-review status, and the approval was granted to Bayer HealthCare Pharmaceuticals.

What happens next

Bayer said the medicine is expected to begin shipping in mid-to-late November, with supplies reaching hospitals and pharmacies in the United States shortly afterwards. Regulators in Europe and Japan are still reviewing the drug. The need is substantial: according to Bayer, about one in 10 stroke survivors has another stroke within a year, and about one in five within five years. For those patients, doctors say, a treatment that cuts that risk without a large rise in major bleeding would be a meaningful step forward, but they stress that anyone who has had a stroke should discuss with their own clinician whether the new option is suitable for them.