The FDA stressed that all patients, especially young adults and those who are improving, should be carefully monitored when treated with Paxil.

The warning letter was accompanied by changes to the labeling of both Paxil and Paxil CR, a controlled-release version of the drug, also called paroxetine.

A recent analysis of clinical trial data on nearly 15,000 patients treated with both Paxil and dummy pills revealed a higher frequency of suicidal behavior in young adults treated with the drug, according to the letter.

The FDA reported that there were 11 suicide attempts -- none resulting in death -- among the patients given Paxil in the trials. Just one of the dummy pill patients attempted suicide.

Caution in Interpreting Results Advised

Given that small number, the results "should be interpreted with caution," the FDA said. Eight of the 11 attempts were made by patients between the ages of 18 and 30. All trial patients suffered from psychiatric disorders, including major depression.

GlaxoSmithKline released its findings following an FDA request that antidepressant manufacturers examine their clinical trial data for any links between the drugs and suicide in adults, company spokeswoman Mary Anne Rhyne said.

"At some point, the FDA is going to say what their analysis shows across the category," Rhyne said, adding of her company's own analysis: "We felt like this was information we wanted to share with physicians."

Careful Monitoring Essential

In the letter to doctors, Dr. John E. Kraus, the company's director of clinical development for clinical psychiatry in North America, said GlaxoSmithKline PLC continues to believe the drug's benefits outweigh its risks.

The FDA stressed that all patients, especially young adults and those who are improving, should be carefully monitored when treated with Paxil.

In 2004, the FDA ordered strong warnings about the pediatric risk of suicidal tendencies put on antidepressant labels, and began analyzing whether adults face a similar risk.

All antidepressants now carry warnings on their labels cautioning patients and doctors of the risk of suicidal behavior.