The survey of GPs in London and the north west of England, carried out as part of a study into depression and substance abuse among young people, found that GPs lacked confidence in their diagnostic skills in both areas.
Of the 62 GPs that replied to the survey, 65 per cent said they were not confident diagnosing substance abuse and 58 per cent lacked confidence in diagnosing depression in children.
Sonita Pobi, National Children's Bureau project development officer, said a key factor was that too few children and young people seek help from their GP for these issues.
The survey found that GPs saw between five and 10 children and young people with depression a year and no more than five cases of substance abuse.
'Children and young people think of GPs as family doctors. PCTs and GPs need to promote their services and especially the emphasis on confidentiality directly to young people,' Ms Pobi said.
She believes GPs' lack of confidence in the area could mean children are not being diagnosed, even when they visit practices.
The survey found GPs were unaware of NICE guidelines relating to children.
Sixty-six per cent of GPs were unaware of advice on substance abuse, and 54 per cent were unaware of depression advice.
'This shows that information is not being filtered down to a GP level which is a matter for concern,' Ms Pobi added.
But Dr Clare Gerada, RCGP drugs spokeswoman, said the findings showed GPs were correctly taking a cautious approach in dealing with these conditions.
'When it comes to children, GPs operate under strict laws and guidelines in terms of treating them.'
She added that GP practices had made progress on dealing with substance abuse.
'The figures show that 30 per cent of practices now have a substance misuse service,' she said.
65% of GPs were not confident diagnosing substance abuse in young people.
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