A major review of antidepressants has found they are largely ineffective and may even be harmful for children and teens.

Key points: Study found only one drug, Prozac, was more effective than a placebo

Study found only one drug, Prozac, was more effective than a placebo Major depression is common children and adolescents

Major depression is common children and adolescents Not treating depression is still more likely to result in harm

The study, published in the prestigious medical journal, the Lancet, reviewed the scientific evidence for 14 different antidepressants in children and young adults.

Lead author Dr Andrea Cipriani from Oxford University in the UK found only one drug, fluoxetine or Prozac, was more effective at relieving depression than a placebo.

Another drug, venlafaxine, was linked to an increased risk of engaging suicidal thoughts.

"The true effectiveness and risk of serious harms such as suicidal thoughts remain unclear because of the small number of trials ... and the selective reporting of findings in published trials and clinical study reports," Dr Cipriani said.

The study reviewed 34 trials with more than 5,000 participants aged between nine and 18.

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Professor Jon Jureidini from the University of Adelaide, who wrote a comment piece about the research, said the findings had "disturbing implications for clinical practice ... as the risk-benefit profile of antidepressants in the acute treatment of depression does not seem to offer a clear advantage for children and adolescents".

The study authors recommend that "children and adolescents taking antidepressants be carefully monitored closely, regardless of the antidepressant chosen, particularly at the beginning of treatment".

Major depression is common in these age groups, with around 3 per cent of children and 6 per cent of adolescents reporting depressive symptoms.

Withholding drugs could also cause harm: Guidelines

Health experts are concerned about a large increase in Australian children and young people being prescribed strong drugs such as antidepressants medications.

A study by University of Sydney researchers in 2014 looked at prescribing patterns for children and adolescents from 2009 to 2012.

The number of children aged between 10 and 14 given antidepressants jumped by more than a third.

University of Sydney's Professor Iain McGregor, a co-author of the 2014 study, said antidepressants were less effective in depressed children and adolescents than in adults.

"Why are we so reliant on meds for our mental wellbeing?" he said.

"We also need to debate whether the benefits of medication outweigh the hazards, particularly in children and in those suffering only mild to moderate psychological distress."

Guidelines for Australian doctors suggest withholding drugs such as antidepressants in children and young people could also be dangerous.

Advice issued in 2005 by the Royal Australian and New Zealand College of Psychiatrists found "not treating depression is more likely to result in harm than is appropriate use of antidepressants".

It found any use of antidepressants in adolescents with major depression should be undertaken only within the context of comprehensive management of the patient.

It recommended starting with a low dose and building up gradually, warning parents and patients about potential side effects, including possible emergence of suicidal thoughts early in treatment, and careful monitoring of the patient.

They also warned that patients should not stop taking the medications suddenly.