Marijuana and IQ: The Adolescent Brain

How does marijuana affect the adolescent brain? Although it’s a controversial subject, most experts agree that regular use of marijuana (and other substances) during the teen years can actually alter the structure of the brain, thus affecting memory, concentration and academic performance.

However, in spite of numerous research studies, there are no firm conclusions about exactly how much marijuana use affects IQ in adolescents.

Studies conducted in New Zealand in 2012 found significant differences in IQ among teens who used marijuana heavily before age 18, compared to those who used the drug only occasionally or not at all.

Similarly, studies at University of Barcelona indicated that chronic users (five out of the last seven days), displayed measurable damage to the areas of the brain that govern planning, impulsivity and abstract thinking, The results were most pronounced in adolescents who started using marijuana before age 16.

Other studies, such as one conducted by Harvard/Massachusetts General Hospital, found similar changes in the area of the brain responsible for judgment, planning and decision making, as well as the area that governs pleasure and reward – the same area associated with addiction.

Although there is considerable evidence that adolescents who begin using pot at young age have more academic and behavioral problems, one significant study called the entire subject into question. The study involved sets of twins over the course of 10 years. Although the twins, including a number of identical twins, were raised in the same home environment, one twin used marijuana while the other didn’t.

The twins were tested between the age of 9 and 12, before they began using marijuana; and again in late adolescence. The results indicated that although the siblings who used the drug displayed decreased cognition at the second test, they also showed similar results in the initial test. Use of marijuana appeared to make no difference.

The question is, if marijuana wasn’t responsible for decreased cognition in the twin that used the drug, what other unexplored factor was responsible? In other words, the young marijuana users may have had problems with cognition long before they began using the drug. Unfortunately, there’s no way to know if 100 percent certainty how results may have differed if one twin had never used the drug.

Other Factors and Reduced IQ

Some experts suggest that use of other substances, including tobacco, may be to blame for reduced cognition in teens that use marijuana. The increased potency of marijuana is also believed to be a factor. Poverty, family environment, peer influence, economic status and educational level of parents may deserve at least part of the equation.

For many researchers, the more important goal is to determine why some adolescents tend to make poor choices, and why they turn to marijuana at such an early age. Heavy use of marijuana is associated not only with a possibility of decreases in IQ, but with poor academic performance, a higher dropout rate, and a greater chance of economic struggles and unemployment in adulthood.

It’s important, however, not to make snap judgments that may result in further marginalization of teens who are already struggling their way through the difficulties of adolescence.

Marijuana and Teens: No “Proven Safe” Level

The teens and early twenties are critical years of rapid brain development. It appears there is no “safe” level of marijuana use, and the earlier the advent of marijuana use, the greater the chance of cognitive difficulties and other problems. However, cognitive changes generally aren’t present in adults who never used marijuana, or in those who waited until they were safely into adulthood.

It’s fair to assume that marijuana during the teens and young adulthood needs careful information and attention as well as advice by professionals.

If you or somebody you love has a problem with excessive use of marijuana or other substances, drug and alcohol treatment or rehab can help. Professional centers also offer assessment of and information on marijuana use. We at Paracelsus are very experienced in doing just that.

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