Johnson & Johnson’s Janssen Pharmaceuticals knew about a faulty device and data in a Xarelto (rivaroxaban) regulatory trial that suggests they put participants at risk, The BMJ reports.

Janssen withheld data about problems with the INRation device from the U.S. Food and Drug Administration, the investigators said. The device monitored patients using warfarin during phase III of the ROCKET AF trial and may have compromised data and patient safety.