Children and young adults who need antidepressants may have an increased risk of suicidal behaviour if they are started on high doses of the drugs, a new study indicates.

US scientists set out to investigate any links between suicidal behaviour and antidepressant doses, including whether age played a role.

They looked at over 162,000 people aged between 10 and 64 who were prescribed antidepressants for depression between 1998 and 2010. All received either a modal (average) dose or higher than modal dose.

The study found that the rate of deliberate self-harm among children and adults aged under 24, was twice as high among those who received higher than average doses to begin with, compared with those who received modal doses.

This increased risk was not found in adults aged between 25 and 64.

"Our findings offer clinicians an additional incentive to avoid initiating pharmacotherapy at high therapeutic doses and to monitor all patients starting antidepressants, especially youth, for several months and regardless of history of deliberate self-harm," the researchers from the Harvard School of Public Health said.

Details of these findings are published in the journal, JAMA Internal Medicine.

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