There is a misconception that has been hovering around the subject of cannabis consumption for quite some time now — that it makes you stupid. However, a team of scientists have discovered that cannabis does not actually reduce a person’s IQ.

A twin study was conducted by Dr. Jessica Megan Ross – alongside a team of researchers – at the Institute for Behavioral Genetics, University of Colorado. Based on the results of the cannabis study, consumption of the plant does not negatively impact cognitive performance. Rather, environmental and genetic factors seem to play a significant role in reducing IQ scores. Moreover, these factors may increase an individual’s likelihood of using weed.

“A co-twin control study is uniquely designed to examine causal relationships,” explains Ross. “Identical twins share 100 percent of their genes and shared environmental factors (e.g., grew up in the same household). Thus, comparing within twin pairs allows us to control for genetics and numerous environmental factors.”

Cannabis and IQ: Refraining from using cannabis won’t safeguard a person’s IQ

A separate longitudinal study conducted in 2012 claimed that cannabis causes neurotoxic effects on teenage brains. The study monitored participants in the age range of 13-38. Following interviews and assessments, researchers found that individuals who used cannabis as a youth saw a decline in cognitive scores for the years that ensued. However, Ross and her team have quashed their findings.

“Our study refutes the results from these studies, which suggest that cannabis use is associated with poorer cognitive function,” said Ross. “Our study did find significant associations between cannabis use and cognition phenotypically. However, when we controlled for genetics, shared environmental factors between twins, and other substance use, these significant associations disappeared.”

Not only did the researchers conclude that cannabis consumption does not harm IQ, but the twin study also revealed that IQ is not protected if an individual abstains from using the plant. To figure this out, the team analyzed cannabis consumption and cognitive performance in 428 pairs of twins; as opposed to individual study subjects. The reason for this was to rule out the possibility of cannabis causing different cognitive changes within twin pairs. 

Cannabis and IQ: Numerous factors could influence cannabis use and lowered cognitive scores

Despite the fact that a clear correlation was noticeable between teen cannabis consumption and low IQ scores – based on the 2012 study – it’s uncertain as to what exactly influences changes in IQ. This left researchers scratching their heads; wondering if something else is causing lowered cognitive scores.

A number of factors could be to blame, such as tobacco consumption, environmental factors, experiencing an ailment – i.e. pain – and lower socioeconomic status. Researchers also felt that consumption of the plant, in whatever form, may increase the chances of a teenager getting involved with “deviant peers”. Being associated with such crowds could deter teens from applying themselves academically, say the researchers.

On the other hand, Ross feels that the University of Colorado’s study had limitations, which essentially made it difficult to draw up an accurate conclusion; not all of the study subjects were heavy cannabis consumers. With that being said, genetic and environmental factors are likely to be the main culprits for negatively impacting cognition and increasing a person’s chances of using cannabis.

“One important study would be to replicate these findings in a sample of heavy cannabis-using twins” proposed Ross. “In general, there is still a lot that we do not know about the positive and negative effects of cannabis. More research is sorely needed to understand various outcomes related to cannabis use.”