Drug or alcohol abuse among children under the age of 15 is a cause and not an effect of a host of health and social problems, research has suggested.

Early drinking and drug-taking raise the future risk of addiction, teenage pregnancy, failure at school, sexually-transmitted infections (STIs) and crime, independently of other factors that might predispose to these outcomes, scientists have determined.

The findings, from a study that followed people for 30 years, are particularly significant because they indicate that drug and alcohol abuse at a young age probably contributes directly to subsequent problems.

While the link is known from previous research, scientists have struggled to tell whether early substance abuse is a cause of later behavioural and health troubles, or a symptom of deprived social or family circumstances that also explain these issues.

The new study, led by Candice Odgers, of the University of California, Irvine, favours the former hypothesis — that “drugs are bad for kids”, rather than “bad kids do drugs”.

Dr Odgers, who conducted the research while at the Institute of Psychiatry at King’s College, London, said: “Findings from this study are consistent with the message that early substance use leads to significant problems in adolescents’ future lives — that drugs are bad for kids — versus the alternative message that young adolescents with a history of problems are just more likely to use drugs early and experience poor outcomes — that bad kids do drugs.

“Even adolescents with no prior history of behavioural problems or family history of substance use problems were at risk for poor health outcomes if they used substances prior to age 15. Universal interventions are required to ensure that all children — not only those entering early adolescence on an at-risk trajectory — require an adequate dose of prevention.”

In the study, which is published in the journal Psychological Science, Dr Odgers investigated a set of 1,000 young people who were born in the New Zealand town of Dunedin in 1972 and 1973.

She found that those who used drugs or alcohol before the age of 15 were between 2.4 and 5 times more likely than their peers to have experienced health or social problems later in life.

The effect applied to dropping out of school, becoming addicted to drugs or an alcoholic, having a criminal convicion, becoming pregnant as a teenager, and testing positive for an STI.

Early use was classified as taking drugs or drinking alcohol on numerous occasions, buying them, or using them at school. This eliminated anyone who drank alcohol at home, or who tried the substances on a one-off basis.

Dr Odgers also compared children deemed at high risk of poor health and social outcomes, such as those with prior behavioural problems or from broken families, with low-risk children.

Low-risk children who used drugs or alochol early still tended to finish secondary school. However, they remained between 2.7 and 3.8 times more likely to have experienced one of the four other social and health problems.

The results, Dr Odgers suggested, mean that it is important to try to prevent early drinking and drug use among all children, not just those from high-risk backgrounds.

Almost 50 per cent of adolescents who used alcohol or drugs before the age of 15 could not have been identified based on child behaviour problems or family risk factors, she said.

The study is indicative of a causal effect, but does not prove it, because children were not randomly assigned to drug-use and non-drug-use groups.

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