A recent UK-based study says that there is no connection between non-habitual teen cannabis use and IQ. The was study conducted on 2,612 children born in the Bristol area of the United Kingdom between 1991 and 1992. Each child’s IQ was tested at the age of 8, then again at the age of 15. Each student at the age of 15 was also surveyed on their use of cannabis for this study.
Although there seemed to be correlation of lower test scores to cannabis use, the correlation was also tied to use of alcohol, tobacco, drugs, and other risky teen behaviors. After these factors were taken into account, researchers found that there was direct correlation between cannabis use and IQ. However, teens who used marijuana heavily did show measurable signs of cognitive damage. This group of heavy users showed a 3% drop in test scores as the result of using cannabis at least 50 times by the age of 15.
“People often believe that using cannabis can be very damaging to intellectual ability in the long-term, but it is extremely difficult to separate the direct effects of cannabis from other potential explanations,” researcher Claire Mokrysz explained. She went on to say that, “The belief that cannabis is particularly harmful may detract focus from and awareness of other potentially harmful behaviours.”
It may come surprising (or not) that alcohol use was found to be strongly associated with IQ decline, but no other factors were found to be predictive of IQ change. This study comes as a significant contradiction to many American studies which try to tie the drug to memory loss or long-term impaired cognition. As recent as 2012, a study by Duke University reported a link between heavy marijuana use and lower IQ scores. The study came under heavy fire by researchers who pointed out significant flaws in their methodology; not surprising considering that Duke is located in the heart of tobacco country. The study was discredited shortly after it’s publication.
With many areas of the world inching toward legalization, proper studies have a tremendous impact on public perception of cannabis. While use is restricted to adults, the prospect of losing brain cells is no less a worry to anyone using cannabis. This new study’s findings may help to curb fears of losing a few IQ points from smoking a joint. It will be presented at the European College of Neuropsychopharmacology next March.
