A Xarelto study on stroke prevention ended early this month after the drug failed to demonstrate any advantage over taking aspirin.

The study focused on Xarelto’s ability to prevent secondary stroke and systemic embolism in patients with a recent embolic stroke of an undetermined source (ESUS). Researchers had enrolled 7,214 patients from 459 sites across 31 countries. Patients were chosen randomly to receive either 15 mg of Xarelto once daily or 100 mg of aspirin once daily.

Drug maker Bayer AG and its development partner, Janssen Research & Development, noted in a press release that while bleeding rates were low overall for test patients, the group taking Xarelto saw an increase in bleeding compared to the group taking aspirin.

While that development may not have been important in other studies, it could be a major factor in why Bayer and Janssen decided to pull the plug here. Xarelto has been implicated in a number of cases where patients experienced extreme bleeding. No antidote exists, which elevates Xarelto side effects to a potentially fatal status.

Based on the observations and analysis of the study’s Independent Data Monitoring Committee, the experiment was halted early because the results displayed similar benefits for both the Xarelto group and the aspirin group. The committee also determined that there would be very little chance of an overall benefit for the Xarelto group if the experiment continued.

“Patients with ESUS currently have limited treatment options and the role of anticoagulants in this area remains uncertain,” said Dr. Joerg Moeller, Member of the Executive Committee of Bayer AG’s Pharmaceutical Division and Head of Development. “We will now analyze the data from [the study] to better understand this outcome and its implications.”

A complete analysis of the Xarelto study on stroke prevention is expected to be presented at an upcoming medical meeting in 2018, Bayer stated in its press release.