Federal health officials have expanded approval of a blood thinning drug to millions of new patients with a common heart problem that can cause deadly strokes and blood clots.

The Food and Drug Administration approved the drug Xarelto for patients with atrial fibrillation, a condition that causes the heart's upper chambers to beat chaotically and ineffectively. About 2.2 million people in the U.S. have the condition, which is a leading cause of stroke.

Xarelto offers a new alternative to warfarin, a 60-year old blood thinner that can be difficult to prescribe. Too much warfarin can cause dangerous internal bleeding, and too little can result in strokes.

Xarelto was previously approved to prevent stroke in patients receiving hip and knee replacements. Bayer and Johnson & Johnson co-developed the once-a-day pill.