The Food and Drug Administration warned yesterday that patients younger than 18 should not take the antidepressant Paxil because of a possible increased risk of suicidal impulses associated with the drug.

The statement from the FDA comes nine days after British regulators issued similar precautions for children and adolescents. The drug, one of GlaxoSmithKline's top sellers, is known as Seroxat in Britain.

The drug generated global sales of about $3.4 billion last year, but it is facing the prospect of generic competition in the United States within the next 18 months.

The medicine has been the subject of increased public concern because of reports of adverse reactions, prompting Britain to set up an expert panel to investigate.

Although Paxil is officially approved for adults only and companies are allowed to promote and market drugs only for approved uses, doctors have had discretion to prescribe Paxil or Seroxat to young people on an "off-label" basis.

Children account for a small portion of patients taking the antidepressant. A total of 4 million prescriptions were written for Seroxat in Britain last year, with 8,000 patients younger than 18 receiving treatment.

New data from clinical trials showed episodes of self-harm and potentially suicidal behavior were 1.5 to 3.2 times higher in patients younger than 18 taking the drug than in those getting a placebo.