TUESDAY, Oct. 19, 2010 (HealthDay News) -- Heavy alcohol and marijuana use puts teenagers at risk for mental deficits that could persist into adulthood, according to a new study.
The researchers found that teens who had abused alcohol and pot scored lower than their abstinent peers on tests measuring a wide range of intellectual abilities.
Robert Thoma, associate professor of psychiatry at the University of New Mexico School of Medicine, the study's lead author, said the researchers wanted to see if heavy substance abuse caused "neuropsychological deficits" in teens similar to those already shown in adult alcoholics and drug abusers.
"The worry is that kids who start drinking early, and drinking heavily, may be affected for their entire life. The data is just beginning to suggest this is true," said Thoma, a clinical neuropsychologist.
Thoma said the study is "too small to make any pronouncements," but is one of the first to show such deficits in teens with substance abuse problems.
Memory was also negatively affected but only by marijuana, not alcohol use, the study found.
Teens who did not use alcohol or drugs but had an alcoholic parent showed deficits on a test measuring "visuospatial ability." Visuospatial ability is the kind of non-verbal thinking involved in creative pursuits such as architecture, music or art.
The study, reported online Oct. 19 in Alcoholism: Clinical & Experimental Research, placed 48 teenagers, aged 12 to 18, into three groups: 19 in a substance-abusing study group, 15 healthy non-users in a control group and 14 non-users whose parents had been alcohol abusers. All 19 substance abusers were diagnosed with alcohol addiction or dependency. Twelve were also diagnosed with marijuana dependency.
The study-group teens, who were two years older on average than the others, reported drinking six to 20 drinks a day during a three-month period prior to the last time they drank. The more alcohol consumed, the worse the teens scored on the battery of tests, especially one measuring executive function.
Executive function includes decision-making, sustaining attention, planning ahead and other skills teens are in the process of developing "and will really need as adults," said Thoma.
The study-group teens reported spending 30 percent of the 90 days surveyed drinking heavily. Those who used marijuana recalled spending 40 percent of that time period smoking marijuana.
"You can imagine how that may affect kids, how important attention and executive function are to developmental tasks," said Thoma. "Kids have to organize themselves, they have to get up early and get to school and sustain their attention to learn some very complicated things."
But Ramani Durvasula said the study might be "comparing apples to oranges" because "kids who abuse drugs and alcohol are different from those who don't," and may have other problems their peers do not.
"When talking about executive function -- control of inhibitions, planning ahead, behavior control -- if these things are already compromised in a child or adolescent, they're going to be more likely to do things like drink," said Durvasula, an associate professor of psychology at the School of Natural and Social Sciences of California State University, Los Angeles.
Noting the large amount of drinking reported by the teens she cited possible problems in their homes.
"Let's face it, when kids are drinking 13 drinks a day (the study average), there's not a lot of parental supervision going on," said Durvasula.
Thoma acknowledged that the data might suggest that kids who had poor executive function were more inclined to drink heavily.
"You have the chicken and the egg problem," said Thoma. "Which came first, the low executive function, which could lead to drinking more, or the heavy drinking, which leads to poor executive function?"
Though not "hard and fast," the correlations suggested that alcohol was the problem, he said, adding, "in science there are levels of how sure you can be about something."
Durvasula also said the six to 20 drinks a day reported by the teens was "implausibly high." She recalled a study she did involving crack-addicted inner-city adult men who only averaged about eight drinks a day.
"They may have had a reporting problem," said Durvasula, also noting the large number of days the teens said they used drugs and alcohol.
The study did not control for socioeconomic level or education, both closely associated with the kinds of mental functioning measured in the study, said Durvasula.
Despite her comments, Durvasula said interventions are needed "both in the schools, and home-based" for teens who are at risk of substance abuse.
Thoma said large longitudinal studies could sort out the causes and effects in drug and alcohol-abusing teens, but noted the research "remains severely underfunded."
For more on teens' drug and alcohol use, visit the U.S. Substance Abuse and Mental Health Services Administration.