As less and less teenagers in the United States smoke cigarettes in previous years, more are turning to use marijuana instead.

A report by the Centers for Disease Control and Prevention revealed that the percentage of students in middle school and high school who exclusively smoked pot in 2013 increased to 10.2 percent as compared to the 4.2 percent in 1997.

How can this affect the brain of teenagers?

A study has shown that smoking marijuana has schizophrenia-like effects – anxiety, social withdrawal, and abnormal levels of dopamine – on adolescents.

A key ingredient of marijuana called delta-9-tetrahydrocannabinol or THC is responsible for these effects, all of which may continue until adulthood.

Dr. Steven Laviolette of Western University in Canada emphasized the fact that adolescence is a critical time for brain development, thus, smoking pot is harmful to teenagers.

Aside from the effects on mental health, scientists have suggested that using marijuana during adolescence leads to a decline in intelligence.

However, a new research involving twins has found that this concept may not be as clear-cut as previously believed.

Can Smoking Pot Really Make You Stupid?

By following more than 3,000 teenage twins, researchers examined whether the use of marijuana is causing reduced memory, decreased intelligence, lower verbal ability and poorer attention in teens, or if these are signs of deeper troubles.

The team focused on twins as they have the same background. Twins also share half or all of their genes. The former is found in fraternal twins, while the latter is found in identical twins.

"In one fell swoop, that allowed us to control for common familial variables and shared genes," said Joshua Isen of the University of Minnesota, a co-author of the study.

Isen and his colleagues tested the twins' intelligence quotient twice at different points in their lives: between 9 to 12 years old – the age before the twins would likely become involved in pot – and again at 17 to 20 years old.

When compared to non-marijuana users, the average change in IQ for marijuana users was about 3.4 to 4 points lower. However, twins who used marijuana did not show a change in their IQ that was any different than the change experienced by their twin who did not smoke at all, researchers said.

"We found there was no difference between twins in terms of how much their IQ changed," said Isen. "The twin who didn't use marijuana showed as much IQ drop as the twin who did."

Tracing The Cause Of IQ Issues To Personal Problems

Dr. Joseph Lee, the medical director for the youth services of the Hazelden Betty Ford Foundation, said teenagers are likely to experience a decline in IQ for several other reasons such as emotional turmoil, family problems, or some other factor.

These teenagers appear more susceptible to marijuana use, alcohol drinking and cigarette smoking at an early age. In turn, they are at greater risk for developing problems later in life, Lee said.

Both Lee and Isen said marijuana use should be a red flag to parents that their child needs help and is struggling.

"This is a big red flag for their life's trajectory," added Lee.

The findings of the study will be featured in the journal Proceedings of the National Academy of Sciences.

Photo: Chuck Grimmett | Flickr

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