Emerging research suggests that while environmental factors influence a teen’s decision to drink alcohol, binge drink, use marijuana and illicit drugs, genetics plays an increasing role with age.
The risk for substance abuse typically begins in early adolescence and increases both in terms of prevalence rates and frequency of use until late adolescence. To better understand the importance of external influences like peers, researchers wanted to account for the influence of genetic factors.
To do this, investigators used a unique sample of twins from Quebec who have been followed since birth. Researchers from Florida Atlantic University and collaborators from the University of Montreal, the University of Quebec, and Laval University in Canada, looked at the relative role of genetics and environment in the development of substance use.
They focused on the critical time between early adolescence (age 13) and late adolescence (age 17) in 476 twin pairs (475 boys, 477 girls).
Researchers examined the relative effects of genetic factors as well as shared environmental factors on the frequency and rate of increase of substance use in adolescents.
Shared environmental factors consisted of environmental experiences, often within the family and at home, that are shared between the two twins. Non-shared environmental factors referred to environmental experiences, often outside the family/home, that are unique to each child.
A study of twins, which compares genetically identical twins with fraternal twins who share only about 50 percent of their genes, provides the best method to separate genetic effects from the environmental effects.
Similar to previous studies, results from the new study show that alcohol and marijuana use increased from early to late adolescence. Genetic as well as shared and non-shared environmental factors explained the amount of substance use; these same factors also partly accounted for inter-individual differences in growth in substance use from ages 13 to 17.
Importantly, the researchers’ analyses also revealed genetic influences that are unique to the growth in substance use. With each passing year, genetic differences between individuals become more and more important in explaining why substance use increases in some adolescents but not in others.
Study findings are published in the journal Psychological Medicine.
“Inheritance becomes increasingly more important in terms of determining drinking and drug use as adolescents get older,” said Brett Laursen, Ph.D., co-author of the study and a professor and graduate studies coordinator in the Department of Psychology at FAU.
“It’s a mistake for us to just assume that peers are the only factor responsible for the growth of substance use.”
Study results suggest that preventive programs should consider personal and familial risk link to substance use, as well as risk factors related to age specific genetic and non-shared environmental influences.
“We can’t take a ‘one-size-fits-all’ approach for intervention programs across age groups,” said Laursen.
“We need to recognize that at each age period different risk factors are associated with substance use, because non-shared and genetic factors change with age. We shouldn’t just assume that the same interventions are going to work at different age periods, because there appears to be different risk factors predicting substance use at different age periods.”
Photo: Brett Laursen, Ph.D., co-author of the study and a professor and graduate studies coordinator in the Department of Psychology in FAU’s Charles E. Schmidt College of Science. Credit: Florida Atlantic University.