Marijuana use before age 18 may significantly decrease IQ

Frequent marijuana usage can negatively affect brain function later in life, according to a study in the Proceedings of the National Academy of Sciences

The recent study, published in late August, showed that participants who used marijuana regularly before the age of 18 had a significantly lower IQ than those who did not.

Amy Richardson, university substance abuse counselor at Wellspring, stated in an email message that she was concerned about marijuana users who begin their usage later in life.

“I am unsure whether this information would change the use habits of those who are over the age of 18,” Richardson said. “Though it should be noted that the adolescent brain continues to develop until about the age of 25, and continued frequent use may have effects on that continued cognitive development.” 

1,037 subjects from Dunedin, New Zealand, were chosen for the study at birth and tested at various points throughout their life. Their brain function was tested at age 13, before any had used marijuana, and then again at ages 18, 21, 26, 32 and 38. 

At the conclusion of the study, researchers found that non-marijuana users gained approximately one IQ point by the age of 38, while the IQ of those classified as cannabis-dependent before the age of 18 dropped an average of five to six points. 

Junior Marissa Personette, president of the Sociology Club, said the study may reveal new information to students.  

“Everyone assumes it would affect memory or concentration,” Personette said. “When students hear that it affects your actual IQ, they might be surprised.”

She said the media presents marijuana as a drug with little to no side effects.

“It’s portrayed as a drug that makes you chill out or lazy, but not dangerous,” Personette said. “If the media doesn’t tone it down, if they don’t emphasize the negative consequences, drug use will never decrease.”

Freshman Timothy Hudert, a member of the National Organization for the Reform of Marijuana Laws, said he thinks the media treats marijuana use in a humorous way, especially in movies. 

The PNAS study revealed the US has a slightly lower rate of marijuana usage than New Zealand, and tests show the potency of the drug in both countries is nearly the same. 

Richardson said according to the annual College Risk Behavior Survey, 19 percent of students at the university said they use drugs other than alcohol. She said marijuana use may be a sign of a deeper problem. 

“Often marijuana use can be a symptom of other underlying factors including depression, anxiety, peer influence, social problems,” she said. “I believe the root problems need to be addressed, whether psychological, social or physical.”

Junior Dana Sivak said she thinks the dangers of marijuana usage should be emphasized.

“[Students] do not believe it’s a hallucinogenic drug, and they say it’s ‘all-natural,’ so they think it’s OK to use it,” Sivak said.