People who began drinking and using marijuana regularly prior to their 15th birthday face a higher risk of early pregnancy, as well as a pattern of school failure, substance dependence, sexually-transmitted disease and criminal convictions that lasts into their 30s.
A study published online by the journal Psychological Science has been able to sort out for the first time the difficult question of whether it's bad kids who do drugs, or doing drugs that makes kids bad.
The answer is both, said Duke University psychologist Avshalom Caspi, who co-authored the report with his wife and colleague Terrie Moffitt. They are part of a team of researchers from the U.S., Britain and New Zealand that analyzed data tracking the health of nearly 1,000 New Zealand residents from birth through age 32.
Half of the study subjects who were using alcohol and marijuana regularly before age 15 were indeed the so-called "bad kids" who came from an abusive, criminal or substance-abusing household and had behavior problems as children.
But the other half were the "good kids" from more stable backgrounds, and they also ended up in poorer health in their 30s.
Caspi said it is clear from these data that adolescent exposure to drugs and alcohol can make a good kid veer off on a bad trajectory. "The good kids who do drugs end up looking like the bad kids who didn't do drugs," Caspi said.
The "good kids," who were without behavior problems as children and didn't have any of the family risk factors, but who began using drugs and alcohol before 15, ended up being 3.6 times more likely to be dependent on substances at age 32. They were also more likely than the other good kids to wind up with a criminal conviction and a herpes infection.
Good and bad, the adolescents who regularly used drugs and alcohol "all had poorer health as adults," Caspi said. "This is consistent with a growing body of evidence that early adolescence may be a sensitive time for exposure to alcohol and other drugs."
He noted however, that the study is not concerned with a kid who tries alcohol a couple of times or who takes a toke at a party. "These are kids who, by the age of 15, are invested in it, purchasing drugs and alcohol and using regularly."
A third of the girls from the "good kids" group were pregnant before age 21 if they had been using drugs and alcohol regularly. That's the same number of pregnancies as the "bad kids" who didn't use drugs. Two-thirds of the "bad kids" who used before 15 were pregnant before age 21. By comparison, only 12 percent of "good" girls who were non-users had early pregnancies.
"Even adolescents with no prior history of behavioral problems or family history of substance use problems were at risk for poor health outcomes if they used substances prior to age 15," said first author Candice Odgers of the University of California-Irvine, who did a post-doctoral fellowship with Caspi and Moffitt. "Universal interventions are required to ensure that all children -- not just those entering early adolescence on an at-risk trajectory -- receive an adequate dose of prevention."
Because the study has tracked these people from birth, "we know pretty much everything about them and we can sort out these things," Caspi said. "We have rich data on these kids' lives and their family situation before they started to do drugs."
The study was funded by the National Institute of Mental Health, the U.K. Medical Research Council, the William T. Grant Foundation, the Health Research Council of New Zealand, and a National Institute on Drug Abuse grant to the Duke University Transdisciplinary Prevention Research Center.
Other authors of the Psychological Science paper include Daniel Nagin of Carnegie Mellon University; Barry Milne of King's College, London; Alex Piquero of the University of Maryland, College Park; Wendy Slutske of the University of Missouri-Columbia; and Nigel Dickson and Richie Poulton of the University of Otago in New Zealand.