The study, which appeared in Proceedings of the National Academy of Sciences of the United States of America, measured differences between 789 pairs of identical adolescent twins over the course of 10 years. In each of the pairs of twins, one of the twins was ultimately a user of cannabis and the other was not.
Researchers chose to conduct the study on identical twins in order to address scientific concerns regarding the sharing of genetics and differences in upbringing among test subjects. Over the course of 10 years, the researchers determined that any loss of IQ points among regular cannabis users was roughly on par with those who did not use cannabis. The study was met with praise from many within the scientific community.
“This is a very well-conducted study…and a welcome addition to the literature,”
said Valerie Curran, a psychopharmacologist at the University College.
However, the study was also met with some caution: Some researchers warned that the study did not remotely conclude that cannabis use is safe for adolescents, while others took issue with the lack of comprehensiveness in the study’s gathering of data and controlling for variables.
The study was conducted by researchers at the University of Southern California – Los Angeles, University of Minnesota – Minneapolis, and the University of Pennsylvania – Philadelphia.