Another study finds that cannabis use is not independently linked with decline in IQ in adolescents

The use of cannabis by adolescents is not independently related to adverse changes in intelligence quotient or executive functioning. This is confirmed once again by the longitudinal data published online before printing in the journal Addiction.

Neuropsychological performance

A team of investigators from the US and UK assessed whether marijuana use is directly associated with changes over time in neuropsychological performance. This was analyzed nationally, involving teenage twins. Thus, the authors reported that "family factors" negatively impacted the cognitive performance of adolescents. Stating that the use of cannabis is not the factor of cognitive decline.

They wrote:

“We found that young people who used cannabis… had an IQ below 18 years old. But there was little evidence that cannabis use was associated with decline in IQ from ages 12 to 18. The poorer IQ and executive functions at the age of 18 were generally not apparent in twin couples of the same family. Which suggests that family background factors explain why adolescents who use cannabis have degraded IQs on executive function tests.

The researchers concluded:

“Short-term use of cannabis in adolescence does not appear to lead to a drop in IQ. Not even an attack on executive functions. Even when the use of cannabis reaches the level of dependence ”.

Their results are consistent with those of several other studies . Including these et here . Thus, we see that the use of cannabis alone during adolescence does not appear to have a significant negative effect. Nor a direct impact on the intelligence quotient.

Socio-economic differences

Caring for widely published study and again oft-cited from New Zealand published in The Proceedings in 2012 found that persistent cannabis use from adolescence to adulthood was associated with a slightly lower IQ at age 38.

However, a follow-up analysis of data published later in the same journal suggested a counter analysis. Particularly in the fact that the observed changes were probably attributable to socio-economic differences, and not to the use of cannabis by the subjects.

A subsequent study by the lead investigator of the first paper added that: The effects of persistent cannabis use among adolescents on academic performance are "Not significant after controlling for persistence of alcohol and smoking".