More than 25 million people in the United States have asthma, a chronic lung disease that inflames and narrows the airways causing recurring periods of wheezing, chest tightness, shortness of breath and coughing. Although several types of drugs are available to treat asthma, long-acting beta agonists (LABAs) are among the most commonly used and work well for most people. However, for a small subgroup of people with asthma, LABAs can cause severe, life-threatening side effects and carry a boxed safety warning from the U.S. Food and Drug Administration.