German pharmaceutical group Bayer said on Monday that its anti-coagulant drug Xarelto, also known as Rivaroxaban, had proved itself effective in preventing strokes in a Japanese study.

A Bayer statement said that phase 3 tests of the treatment showed it was as effective as warfarin, a leading blood thinner also used by people that could suffer strokes following surgery.

"Rivaroxaban demonstrated non-inferior safety and that there were numerically fewer intracranial hemorrhages versus warfarin," the statement said.

Bayer applied in April for Japanese approval to market the drug that it developed jointly with Johnson & Johnson, which already sells Xarelto in the United States.

Bayer estimates the treatment's sales potential at more than two billion euros ($2.9 billion) per year.

Xarelto is now sold in more than 110 countries and is often prescribed for patients that have had hip or knee replacements.