GlaxoSmithKline (GSK) has sent a letter to doctors warning them that there could be an elevated risk of suicidal behaviour in adults under 30 taking its antidepressant, Seroxat (sold as Paxil in the US).

Having reanalysed data from clinical trials involving almost 15,000 people, the firm said there was a higher frequency of suicidal behaviour in young adults treated with the drug for depression than in those taking a placebo.

The new analysis comes after the US Food and Drug Administration asked all manufacturers of anti-depression treatments to evaluate whether their products increased the risk of suicidal thoughts among adults.

The FDA said its review of antidepressants is not yet complete and patients taking such drugs should be carefully monitored for worsening of depression and suicidal thinking. It also said it is essential that patients on Seroxat don't stop taking it suddenly.

In a statement, GSK said that ìall of the reported events of suicidal behaviour in the adult patientsÖ were non-fatal suicide attempts, and the majority of those attempts were in younger adults aged 18 to 30î.

ìThis new analysis reinforces existing medical guidance to closely monitor patients during treatment,î said a GSK spokeswoman. ìThis is especially the case in patients with depression, and the under 30 year olds.î

In 2004, the Medicines and Healthcare products Regulatory Agency (MHRA) issued a warning that children taking Seroxat in clinical trials were nearly three times more likely to attempt suicide than those on placebo and recommended that the drug should not be prescribed to children.

In August 2005, Seroxat was linked to increased suicide risks in adults in a study by researchers at Oslo University. They wrote in the BMC Medicine journal that an analysis of trials involving more than 1,500 patients found seven suicide attempts among those taking the drug and only one among those taking a placebo.

In the latest analysis, GSK found that the frequency of suicidal behaviour was higher in patients taking Seroxat - 11 out of 3,455 compared to one out of 1,978 on placebo. GSK said the findings should be interpreted with caution, due to the small numbers involved.

Seroxat, which has lost its market exclusivity, had first-quarter sales of £161m ($304m).