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US warnings about the risk of suicide in young people prescribed antidepressant medication may have backfired, research suggests.

A study, in the British Medical Journal, showed a sudden fall in antidepressant prescriptions and a rise in suicide attempts after media reports of the connection.

The team at Harvard Medical School said the unintended effect was "disturbing".

Experts said similar changes had been seen in other countries.

In 2003, there were concerns about an increased suicide risk from some antidepressants. It led to the US Food and Drug Administration changing the medicine warnings and widespread media reports.

However, there was concern that the reports were exaggerated and missed out the benefits of antidepressants.

Big fall

The study, which followed 2.5 million teenagers and young adults between 2000 and 2010, showed an immediate impact of the warnings.

Prescriptions fell by a third in teenagers and by a quarter in young adults.

The number of suicide attempts increased by 22% in teenagers and 34% in young adults. Overall it led to an additional 77 attempts, the researchers estimated.

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The report concluded: "It is disturbing that after the health advisories, warnings and media reports about the relation between antidepressant use and suicidality in young people, we found substantial reductions in antidepressant treatment and simultaneous, small but meaningful increases in suicide attempts."

One of the researchers, Prof Stephen Soumerai, said: "This is an extraordinarily difficult public health problem, and if we don't get it right, it can backfire in serious ways.

"These drugs can save lives. The media concentrated more on the relatively small risk than on the significant upside."

'Powerful impact'

Prof Keith Hawton, the director of the centre for suicide research at the University of Oxford in the UK, said: "The results of this study are important.

"Such findings illustrate the powerful impact that such announcements can have on clinician behaviour.

"Until now there has not been convincing evidence that such changes in practice have affected suicidal behaviour.

"The US study suggests that this may have happened, although fortunately without evidence of an increase in actual suicides."

Dr Christine Lu, of Harvard, told the BBC: "There are several lessons for us to consider. Drug risk communication is a big field and we need to be better next time. Any communication can have intended and unintended consequences.

"And I think a key message is to remind ourselves not to consider only the new evidence on any drugs, but also consider its risk and the benefits, and undertreating the original condition itself."