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.