By Mary O’KEEFE

Researchers at Harvard-affiliated McLean Hospital have shown that those who start using marijuana at a young age are more impaired on tests of cognitive function than those who start smoking at a later age.

In a paper that was presented Monday at the annual meeting of the Society for Neuroscience in San Diego, Staci A. Gruber, PhD, reported that subjects who started using marijuana before age 16 made twice as many mistakes on tests of executive function, which includes planning flexibility, abstract thinking and inhibiting inappropriate responses as those who began smoking after age 16.

The conclusion of this study reaffirms others’ findings of those who abuse marijuana at an early age.

“There are several studies on [this affect],” said Glendale Police Sgt. Tom Lorenz.

Lorenz travels throughout the country speaking on drug use. He uses it as an example of how art can truly imitate life.

“The child’s brain continues to develop until they are 21-to-24 years old. The fact that we have a law that you don’t drink until you are 21 is not just a random number chosen,” he said.

The study also found that early-onset users also smoked three times as much marijuana per week and twice as often compared to the later-onset users.

“Our data suggests that the earlier you begin smoking, the more marijuana you smoke and the more frequently you smoke,” stated Gruber who is the director of the Cognitive and Clinical Neuroimaging Core at McLean and assistant professor of Psychiatry at Harvard Medical School.

The subjects of the study were given a battery of neurocognitive tests assessing executive function. One of the tests involved sorting different cards based on a set of rules given. During the test the rules changed without warning and subjects must adjust their responses to the new rules, according to McLean Hospital statement.

“Study after study has shown that early substance abuse does impair the development of a young person’s brain,” Lorenz said.

He added that this could hold true with abuse of any drug including prescribed medication.

“Young people are prescribed medication but are [monitored] and it is medically driven,” he added. “What this study is talking about is abusing [marijuana]. Prescribed drugs are a whole separate issue.”

Glendale officer Joe Allen has years of experience dealing with those who abuse drugs. He said this study is no surprise to him.

“I see young kids [who abuse marijuana] and their ambition, motivation and drive lessens,” Allen said.

He estimated the average age kids begin using marijuana is about 12 years old. This seems to be in line with the national average. In 2009, a survey of kids 12 years old or older found that 16.7 million had used marijuana in the past month. The rate of current marijuana use among children from 12 to 17 increased from 6.7% in 2008 to 7.3% in 2009.

Lorenz hoped the study would bring home the message that abuse of marijuana does have an affect on a developing brain.

“Given the prevalence of marijuana use in the U.S. these findings underscore the importance of establishing effective strategies to decrease marijuana use, especially in younger populations,” state Gruber.

  GPD, research