[LindaT]

WASHINGTON (CNN) -- The U.S. Food and Drug Administration has approved a new antidepressant called Lexapro, a drug that researchers say may be more powerful and faster-acting than similar antidepressants.

Lexapro becomes the sixth drug in a class of antidepressants that includes the well-known names Prozac, Paxil, Zoloft, Luvox and Celexa.

Lexapro is very similar to Celexa, but possibly more powerful and faster-acting, according to researchers who have worked with it.

"These are modest benefits, but they're incremental advances over the other medicines within this class that are available," said Dr. Philip Ninan of Emory University Medical Center.

The side effects associated with antidepressant drugs include stomach upsets, headaches, and sexual complications. They show up in about 10 percent of the people who take the drugs.

With Lexapro, said researchers, the percentage of people who have those side effects is about 5 percent, or half the number associated with the other five drugs.

"It seems to have less side effects than Celexa at a comparable dose," Ninan said, who added it may also give relief quicker than similar drugs.

He described Lexapro as "another option" that doctors can prescribe as an alternative for patients who cannot take the other five antidepressants without suffering side effects.

An estimated 18.8 million American adults suffer from a depressive illness.

The six antidepressants are in a class of drugs called selective serotonin re-uptake inhibitors, or SSRIs, which work by allowing more of a brain chemical called serotonin to remain in the brain.

Lexapro is expected to be in pharmacies by September 5, according to the drug's manufacturer, Forest Laboratories Inc.