The Food and Drug Administration has approved the first drug to treat panic disorder, a mental illness expected to strike about 3 million Americans during their lives, it was announced Thursday.

The drug, alprazolam or Xanax Tablets, has been on the market for about 10 years for reducing general anxiety. However, until the action by the FDA, it could not be marketed for panic disorder.Xanax is first and only drug in the United States specifically indicated for treatment of panic disorder, FDA spokeswoman Eva Kemper said. Doctors can prescribe government-approved drugs for any use they want and many in recent years have been prescribing Xanax for panic disorder, but insurers often refuse to pay for anything but FDA-sanctioned uses.

An estimated 3 million Americans - between 1 percent and 2 percent of the population - will suffer from panic disorder in their lifetimes, said The Upjohn Co., of Kalamazoo, Mich., which makes Xanax. The disorder usually surfaces in early adulthood, and is often associated with intense fear of objects or situations, like being in a crowded room.

"When unrecognized or untreated, panic disorder can profoundly disrupt people's lives," Gerald Klerman, a psychiatric researcher of Cornell University Medical College in New York, said in a statement.

Panic disorder is characterized by repeated attacks of intense fear that causes chest pain, shortness of breath, dizziness, trembling, nausea and other signs of physical distress. People suffering an attack say they often feel like they are dying or losing their minds.