Decline in IQ linked to frequent or dependent use of cannabis use in youth

Cohen's d=-0.132 is considered a very small effect size. In other words: The effect is statistically reliable, significant, and disagreements between studies are very low, but not that big.

>The approximately 2-point decline in IQ in adolescent-onset frequent cannabis users is not to be clinically significant

In a population level this might be part of the explanation, but we would have to know the correlation between prevalence of use of cannabis and IQ decline in the population. In developed nations there is trend where IQ drops 0.2 points per year (2-points per decade) since mid 1990s. In developing countries IQ increases 3-points per decade as Flynn-Effect still works there.

Re: Decline in IQ linked to frequent or dependent use of cannabis use in youth

#5

Post by metalman » Sat, Jun 27, 2026, 9:17 AM UTC

Rastas say that "cannabis" isn't for stupid people, which is an observational conclusion. There are other sometimes profound and imediate negative effects cannabis consumption

Re: Decline in IQ linked to frequent or dependent use of cannabis use in youth

#6

Post by damnesian » Sat, Jun 27, 2026, 9:36 AM UTC

Like any tool, it depends on how you use it. As a teenager, I used it to paint and write. It opened many doors. I found inner expression that was not possible otherwise.

The measures used in the study are not absolutes and only a fragment of what constitutes human intelligence.

Re: Decline in IQ linked to frequent or dependent use of cannabis use in youth

#7

Post by pixel_popping » Sat, Jun 27, 2026, 11:18 AM UTC

Cannabis is better enjoyed as a late adult, maybe >25 years old, as almost any drugs. I wouldn't advise it to the youth, it can really ruin your concentration years later.

Re: Decline in IQ linked to frequent or dependent use of cannabis use in youth

#8

Post by u1hcw9nx » Sat, Jun 27, 2026, 2:15 PM UTC

damnesian wrote: post #6

Like any tool, it depends on how you use it. As a teenager, I used it to paint and write. It opened many doors. I found inner expression that was not possible otherwise. The measures used in the study are not absolutes and only a fragment of what constitutes human intelligence.

IQ as measured correlates positively with all talents.

There is moderate correlation with arts, sports and athletic talents (weak for basic athleticism, moderate to strong for elite levels.) With music and writing the correlation is even better, from moderate to strong. High IQ increases the ability for inner expression, or expression of any kind.

People seem to forget that IQ is a factor as in factor analysis. It does not measure a "thing". It measures variability among observed, correlated variables.

Re: Decline in IQ linked to frequent or dependent use of cannabis use in youth

#9

Post by youdonow » Sat, Jun 27, 2026, 6:03 PM UTC

solumunus wrote: post #2

I feel it.

You feel 2 IQ points?

Even proponents of IQ tests admit they have a margin of error 3-5 points. Meaning you can swing on IQ tests beyond this threshold on the same day.

I'm guessing bad sleep or missing a meal the night before will swing your IQ significantly more than 2 points.

Re: Decline in IQ linked to frequent or dependent use of cannabis use in youth

#10

Post by youdonow » Sat, Jun 27, 2026, 6:06 PM UTC

u1hcw9nx wrote: post #8

damnesian wrote: post #6

Like any tool, it depends on how you use it. As a teenager, I used it to paint and write. It opened many doors. I found inner expression that was not possible otherwise. The measures used in the study are not absolutes and only a fragment of what constitutes human intelligence.

IQ as measured correlates positively with all talents. There is moderate correlation with arts, sports and athletic talents (weak for basic athleticism, moderate to strong for elite levels.) With music and writing the correlation is even better, from moderate to strong. High IQ increases the ability for inner expression, or expression of any kind. People seem to forget that IQ is a factor as in factor analysis. It do…

That's why all of your favorite, and history's greatest, visual artists, writers, athletes, musicians and aesthetes stay far away from any mind altering substances!

Erdos famously stayed far away from amphetamines to preserve those precious 2 IQ points.