LONDON (Reuters) - A medical journal criticized British drugmaker GlaxoSmithKline on Thursday for delaying access to key data from a trial of its antidepressant Seroxat that would have shown earlier that it is neither safe or effective in adolescents.

The widely used medicine, known generically as paroxetine, is linked to an increased risk of suicide in young people and has carried a Food and Drug Administration (FDA) "black box warning" advising against its use in adolescents since 2004.

Britain's Medicines and Healthcare Products

Regulatory Agency recommended in 2003 that antidepressants like Seroxat should not be used in children or adolescents, and European regulators followed suit in 2005.

But, writing in the British Medical Journal (BMJ), researchers who re-analysed a Seroxat study first published in 2001 said the drug's dangerous side effects could easily have been highlighted years earlier.

"This is fundamentally about correcting the scientific record," said Peter Doshi of the University of Maryland School of Pharmacy in the United States, a BMJ associate editor.

The re-analysis used previously unseen data from records of patients involved in the trial and found that at least 12 out of 93 children taking the drug had developed suicidal thoughts.

The 2001 Seroxat study, funded by GSK, is the first trial to be re-analysed under a BMJ initiative called Restoring Invisible and Abandoned Trials (RIAT), designed to encourage pharmaceutical firms to publish or correct abandoned or misreported drug trials.

The aim is to ensure doctors and patients have complete, accurate information to make treatment decisions.

GSK's original study was published in the Journal of the American Academy of Child and Adolescent Psychiatry in 2001 and reported paroxetine as safe and effective for adolescents.

GSK -- which in 2012 was fined $3 billion for fraudulently promoting several drugs, including paroxetine -- responded to the BMJ re-analysis by saying it had helped by providing access to detailed data from the original trial.

"This reflects our commitment to data transparency," the company said, adding it had now pledged to publish the results of all its studies, whether they are positive or negative.

It also agreed Seroxat should not be given to young people.

"There is an increased risk of suicidality in pediatric and adolescent patients given antidepressants like paroxetine," GSK said. "This is widely known and clear warnings have been in place on the product label for more than a decade."

Doshi argued, however, that the case showed why full patient data should published alongside original scientific analyses.

"What would have happened if this data were available 15 years ago when the study was originally published?," he said. "Would the black box warnings from the FDA have come earlier?"

(Reporting by Kate Kelland; Editing by Mark Heinrich)