Adolescents who lack self–control, have attention deficits, or demonstrate poor “executive function” are more likely to experiment with a greater variety of drugs and alcohol. However, they are not more likely to become dependent as young adults, according to a new CU Boulder study of twins. “Some people assume that if you try something in adolescence, you are on a path you are never going to come back from – sort of the gateway drug hypotheses,” said first author Daniel Gustavson, who conducted the study as a graduate student at the Institute of Behavioral Genetics. “Our data do not support this and instead suggest it could just be about experimenting.”

The research also found that genetics strongly influence poor executive function – or a lack of higher–level cognitive abilities that control goal–oriented behavior – and the tendency to experiment with substances.

The authors looked at 846 twins, asking them at age 17 how many of 15 different substances (including tobacco, alcohol, marijuana, cocaine, amphetamines and hallucinogens) they had used and how often during a six–month span. They also measured signs of dependence.

Then they had them complete nine tasks to measure executive functions, such as the ability to switch between tasks without losing focus, or resist doing something they were used to doing automatically.

The participants repeated the tests at age 23, representing an age span (from 17 to 23) that’s considered critical in the progression of substance use. Two key findings emerged.

Identical twins scored almost identically on executive function tests, while fraternal twins showed broad variation, suggesting that executive function in young adults is driven by genetics.

Those with poor executive function tended to use more substances more frequently at age 17. But by age 23 the difference between them and their peers with greater executive function had diminished.

At neither age did those with poor executive function show greater signs of dependency.

“Our results suggest that poor executive function is most related to early experimentation with substances rather than the tendency to escalate use,” the authors conclude in the paper, published in February in the Journal of Abnormal Psychology. They added that poor executive function may play “little or no role in dependence/abuse in adolescence.”

Previous research has shown a link between poor executive function and substance use. However, it has been unclear whether substance use impairs executive function, or poor executive function leads to substance use. “This study suggests that genetic influences may cause both,” said Gustavson, now a postdoctoral researcher at the University of California, San Diego.

The study also suggests that while brain regions related to executive function may be involved in driving experimentation and risky behavior, different regions governing regulation of the brain’s reward system are likely involved in addiction to specific substances.

Senior author Naomi Friedman, an assistant professor in the CU Boulder department of psychology and neuroscience, said the findings could ultimately help inform prevention and treatment programs. For parents, she said, it can serve as both a caution and a comfort.

The study suggests that behavioral problems indicative of poor executive function can be a red flag that a child may also be more prone to experimenting with risky behaviors as a teen.