June 27, 2026
High thoughts, low scores?
Decline in IQ linked to frequent or dependent use of cannabis use in youth
Study says teen weed may shave off a couple IQ points — and the comments are blazing
TLDR: A review of seven studies found frequent teen cannabis use was linked to an average drop of about 2 IQ points. Commenters instantly split into two camps: people saying “yep, been there” and others arguing the effect is small and intelligence is bigger than one number.
A new study is throwing fresh fuel on one of the internet’s favorite forever-fights: does teen cannabis use actually make you less sharp? The researchers reviewed seven long-term studies and found that young people who used cannabis frequently or became dependent showed an average drop of about 2 IQ points over time. That’s not a Hollywood-style brain wipe, but it was enough to send the comment section into full "well, obviously" vs "hold on, that’s tiny" mode.
The strongest reaction came from the stats crowd, who immediately slammed the brakes on panic. One commenter pointed out that the effect size was very small, basically saying: yes, the result looks real, but let’s not act like this turns honor students into houseplants. Then came the lived-experience brigade. One person bluntly posted, "I feel it," which is probably the shortest and most devastating review of a scientific paper imaginable. Another took the softer middle road: cannabis may be fine later in adulthood, but using it young can mess with concentration for years.
And of course, the thread had its philosophical rebels. One commenter argued cannabis helped them paint, write, and unlock inner expression, insisting that IQ tests only capture a sliver of human intelligence. That sparked the classic online culture clash: book smarts vs creativity, statistics vs vibes. Even the jokes had bite, with people treating the study like a giant subtweet of their teenage selves. In other words: the paper brought data, but the comments brought the drama.
Key Points
- •The article describes a systematic review and meta-analysis of longitudinal studies assessing whether frequent or dependent cannabis use in youth is associated with IQ decline.
- •The review included seven cohort studies with 808 cases and 5,308 controls, using pre- and post-exposure IQ measures in non-treatment-seeking samples.
- •The pooled result showed a statistically significant association between frequent or dependent youth cannabis use and IQ change, with Cohen's d = -0.132 (95% CI -0.198 to -0.066; p < 0.001).
- •Statistical heterogeneity across the included studies was very low (I2 = 0.2%), and study quality was rated moderate to high.
- •The authors interpret the effect as an average decline of about 2 IQ points after cannabis exposure in youth and call for longer follow-up studies.