Written by Loren Grush
While smoking marijuana is sometimes touted for its ability to dull pain, research has emerged showing that it also significantly dulls the mind – especially in teenagers.
A new study of more than 1,000 children in New Zealand, following them from birth to the age of 38, found that those who began using cannabis during their adolescence showed a decrease in their general intellectual ability, as measured by IQ tests, from childhood to adulthood.
A person's IQ - or intelligence quotient - does not measure a person's amount of knowledge, but rather represents a person's ability to comprehend concepts, as well their capacity to process information. Typically, IQ does not change significantly over the course of a person's life, unless as a result of severe brain damage from trauma or disease.
Although previous research has found adolescent cannabis use to have an effect on IQ, this is the first study to rule out pre-cannabis performance explaining the results. Researchers initially tested the participants at the age of 13 – before they began using cannabis – ultimately comparing this IQ to later tests throughout their adulthood.
While drug tests were not used in this study, detailed questionnaires given to the participants at five different ages throughout their lives helped to establish their marijuana use.
“We assessed cannabis use in two ways,” the study's lead author Madeline Meier, of the Department of Psychology and Neuroscience and Duke Transdisciplinary Prevention Research Center at Duke University, Durham, told FoxNews.com. “At [various] ages, they were asked to go back and report for that past year how frequently they used cannabis. They were also given diagnostic interviews, where we diagnosed cannabis dependence. Dependence generally reflects someone who has been using cannabis and experiencing health, social and/or legal problems – but are still continuing to use.”
Each individual was categorized into one of various groups depending on their cannabis use and dependence. The two main groups the researchers focused on were adult-onset cannabis users and adolescent-onset cannabis users.