Teens who are heavy users of alcohol or marijuana end up with more than a high: The chemicals damage the area of their brains that controls judgment, decision-making and social skills, a new study shows.

The research, led by Robert J. Thoma of the University of New Mexico School of Medicine, produced results in line with studies over the last decade that linked adolescent binge drinking and marijuana use to brain impairment.

The new study links heavy drinking to damage in the brain's frontal lobe during a crucial period of development. The researchers said the findings show how alcohol disrupts processes that sharpen attention and planning skills.

The study will be published in the January 2011 issue of the journal Alcoholism: Clinical & Experimental Research.

The teenage brain, on drugs

The findings were based on a battery of psychological tests. The researchers found that as drinking intensity increased, teenagers demonstrated a significantly decreased ability to pay attention and respond appropriately to stimuli in their environment.

Researchers studied 19 adolescents who had a history of substance abuse or dependence, and a control group of 15 teens with neither a personal nor family history of substance abuse.

The research differed from other work by also including 14 teenagers who had not used drugs or alcohol but whose families had a history of substance abuse. These teens demonstrated poorer spatial skills than others.

While none of these teens showed symptoms of fetal alcohol syndrome, the researchers said the spatial problems may stem from the teens' prenatal exposure to alcohol. Their inclusion in the study allowed researchers to disentangle the effects of such exposure from the effects of teenage use of alcohol.

The researchers also found, as other studies have, a strong link between marijuana use and memory problems.

Thoma, a clinical neuropsychologist and associate professor of psychiatry, writes that prevention and treatment of teenagers' substance abuse are important because some neural development takes place during late adolescence.

Susan Tapert, a professor of psychiatry at the University of California, San Diego, conducted similar research over the last several years and, like Thoma, found heavy drinkers could regain at least some lost brain function after they abstained.

"It's always reassuring, in science of this nature, when we see similar findings come from different researchers and study subjects," Tapert told MyHealthNewsDaily.

Thoma said: "Recovery of function with cessation of drinking is a well-established finding in adults. And there is reason to believe the same would hold in youth, who tend to be resilient." If damage is caused by alcohol, he said, the damage is likely to lessen when a person reduces drinking or abstains.

What about occasional use?

Future research should focus on the effects of light or moderate alcohol consumption by adolescents, which has not yet been studied, said David J. Hanson, professor emeritus of sociology at the State University of New York at Potsdam.

People of some ethnic groups, including Jews, Greeks, Italians, French and Spaniards, regularly drink alcohol in moderation from a very young age, Hanson told MyHealthNewsDaily, and there is no evidence to suggest they suffer any brain deficits compared to other groups.

Thoma said he and his team plan to continue their research to determine if alcohol-induced brain damage is dose-dependent, and whether intervention should be recommended for modest alcohol use.

The study was funded by the National Institute on Alcohol and Alcoholism and the Mind Research Network, an independent, nonprofit organization dedicated to research on mental illness and brain injury.