July 2 (HealthDay News) -- Multaq (dronedarone) tablets have been approved by the U.S. Food and Drug Administration to promote a normal heart rhythm in people with atrial fibrillation or atrial flutter. These conditions cause the heart to beat too quickly and can prevent it from pumping blood correctly.

The drug's label, however, will contain a "black box" warning that the medication could cause deadly reactions in people with recent severe heart failure, the agency said Thursday in a news release.

In clinical testing involving more than 4,000 people, Multaq lowered the rates of cardiac hospitalization or death from any cause by 24 percent, compared to an inactive placebo, the FDA said. The most common side effects were diarrhea, nausea, vomiting, fatigue and weakness.

Multaq is produced by French drug maker Sanofi-Aventis.