HUNTSVILLE, TX (3/20/14) -- Parents who use alcohol, marijuana, and drugs have higher frequencies of children who pick up their habits, according to a study from Sam Houston State University.

The study, "Intergenerational Continuity of Substance Use," found that when compared to parents who did not use substances, parents who used alcohol, marijuana, and other illicit drugs were significantly more likely to have children who used those same drugs. Specifically, the odds of children's alcohol use were five times higher if their parents used alcohol; the odds of children's marijuana use were two times higher if their parents used marijuana; and the odds of children's other drug use were two times higher if their parent used other drugs. Age and other demographic factors also were important predictors of substance use.

"The study is rare in that it assesses the extent to which parent's substance use predicts use by their children within age-equivalent and developmentally-specific stages of the life course," said Dr. Kelly Knight of the College Criminal Justice's Department of Criminal Justice and Criminology. "If a parent uses drugs, will their children grow up and use drugs? When did the parent use and when did their children use? There appears to be an intergenerational relationship. The effect is not as strong as one might believe from popular discourse, but when you measure it by developmental stage, it can provide important information on its impact in adolescence and early adulthood, specifically."

The study examined the patterns of substance use by families over a 27-year period. It documents substance use over time, giving a more complete understanding of when substance use occurs, when it declines, and the influence of parents in the process.

According to the National Survey on Drug Use and Health in 2011, about 22.6 million Americans age 12 years and older said they used illicit drugs in the last month. Other studies show that drug use is associated with reduced academic achievement, lower employment rates, poorer health, dependency on public assistance, neighborhood disorganization, and an increase in the likelihood of involvement in crime, criminal victimization and incarceration. The cost of drug use in this country from lost productivity, healthcare, and criminal justice is nearly $600 billion.

By plotting the life course of substance use within families, the study may be a valuable tool for the development of intervention programs. The study suggests that if substance use can be curtailed in adolescence, it may help to curb its prevalence in future generations.

The study also helps pinpoint the use of different illicit substances over the span of a lifetime, including its emergence in adolescence and when that use may decline. For example, marijuana and other drug use is most prevalent in adolescence and generally declines before or at age 24. Alcohol use continues to increase throughout adolescence and young adulthood, and then remains relatively steady over the lifetime.

These findings come from the National Youth Survey Family Study, which has collected data from three generations over a 27-year period. The analysis is based on 655 parents and 1,227 offspring from 1977 to 2004.

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