Marijuana use robs teens of about 8 IQ score points, lower than average, when they become adults, according to a new study. They also show symptoms typically associated with Alzheimer's disease after researchers observed more than 1,000 people in New Zealand for 20 years.
"Somebody who loses 8 IQ points as an adolescent may be disadvantaged compared to their same-age peers for years to come," Lead researcher Madeline Meier, a post-doctoral researcher at Duke University, said in a statement.
The study found that those who are persistent and smoke the drug more than once a week before they reach the age of 18, experience the symptoms.
Meier and a team of international colleagues said a long-range study cohort of more than 1,037 New Zealanders born in 1972-1973 found about 5 percent were considered marijuana-dependent, or were using more than once a week during their teens and before age 18.
A dependent user is one who keeps using despite significant health, social or family problems, Meier said.
At age 38, all of the study participants were given a battery of psychological tests to assess memory, processing speed, reasoning and visual processing.
The study, published in the Proceedings of the National Academy of Sciences, found an average decline in IQ of 8 points when their age 13 and age 38 IQ tests were compared. Quitting pot did not appear to reverse the loss, the study said.
The lower IQ among persistent marijuana users could not be explained by alcohol or other drug use or by having less education, Meier said.
"Somebody who loses 8 IQ points as an adolescent may be disadvantaged compared to their same-age peers for years to come," Lead researcher Madeline Meier, a post-doctoral researcher at Duke University, said in a statement.
The study found that those who are persistent and smoke the drug more than once a week before they reach the age of 18, experience the symptoms.
Meier and a team of international colleagues said a long-range study cohort of more than 1,037 New Zealanders born in 1972-1973 found about 5 percent were considered marijuana-dependent, or were using more than once a week during their teens and before age 18.
A dependent user is one who keeps using despite significant health, social or family problems, Meier said.
At age 38, all of the study participants were given a battery of psychological tests to assess memory, processing speed, reasoning and visual processing.
The study, published in the Proceedings of the National Academy of Sciences, found an average decline in IQ of 8 points when their age 13 and age 38 IQ tests were compared. Quitting pot did not appear to reverse the loss, the study said.
The lower IQ among persistent marijuana users could not be explained by alcohol or other drug use or by having less education, Meier said.
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