New research is calling into question the findings of a 2012 study that linked heavy marijuana use early in life to long-term cognitive impairment. Published in the Proceedings of the National Academy of Sciences, the latest analysis involving more than 3,000 adolescents concluded that teens who used marijuana regularly saw no more of an IQ dropoff over time than their non-using twin siblings.
The latest research analyzed findings of two previous studies that had looked at the possible relationship between marijuana use and cognitive decline. This new analysis suggested that a 2012 Duke University study that linked frequent marijuana use to intellectual decline did not consider other confounding factors that could have contributed to decreasing IQ in its sample, such as the presence of other substance use and mental illness.
The lead author of the new study has stated that while the 2012 study results are not discredited, the conclusion that had been drawn from its results should be considered premature.