Jon Jureidini, head of the department of psychological medicine at the Adelaide Women's and Children's Hospital, said that international research suggested these drugs could be harmful to children.

"There certainly is now evidence that there is an increase in suicidal thinking and suicidal actions with the use of these drugs," Dr Jureidini said.

"The evidence for their harmful effects is good and the evidence for their efficiency (in treating depression) is poor."

This concern centres on one class of drugs, known as Selective Seratonin Re-Uptake Inhibitors.

The Therapeutic Goods Administration wrote to doctors in March warning them about possible increases in suicidal behaviour linked to these drugs.

No SSRI was registered in Australia for the treatment of depression in children and adolescents, it said.

Despite this, estimates from the General Practice Statistics and Classifications Unit at the University of Sydney put the number of prescriptions to children at about 70,000 in 2003-4.

While the overall number of prescriptions has fallen, the prescription rate for anti-depressant drugs to people under 18 rose by about a third in this time.

Helena Britt, who led the study, said this did not necessarily reflect the number of children using anti-depressants in Australia.

"The average number of visits to a GP is five so you can never say that there are this many kids on these drugs," Professor Britt said.

The figure for 2003-04 also relied on a smaller sample group than previous years and, as such, was less certain, she said.

Choung-Siew Yong, of the Australian Medical Association, said an increasing number of people were being diagnosed with depression.

"Depression in adults and children is something that has been unrecognised and undiagnosed in the past. I think that is one reason why there is an increase in prescriptions," he said.

While doctors were increasingly aware of concerns over the use of SSRIs, it was too early to expect this to be reflected in the figures, Dr Yong said.