Last Updated on 19th September 2020

It’s official – cannabis use does not make you stupid. A 2012 study that found that cannabis lowers IQ has just been refuted by new research. What is notable is that the scientists involved in the original 2012 research has reversed her earlier findings. Madeline H. Meier’s 2012 study in Proceedings of the National Academy of Sciences claimed cannabis use in youth can permanently lower the person’s intelligence quotient, or IQ.

Media piled on to negative findings

Mainstream news widely reported the research at the time. Time magazine summarized the findings as, “Heavy marijuana use is associated with cognitive decline in about 5% of teens, according to a new study, which suggests that the heaviest users could lose 8 IQ points.”

Even when the research was originally published, the same journal published two different rebuttals that said socioeconomic status and/or personality traits better explain the correlation between childhood cannabis use and lower IQs. This prompted the original researchers to respond in what became a public spat in clinical circles.

Prohbtd websites reports this week that since then, Meier moved from Duke University to Arizona State University, and she led a follow-up study that included three of the original co-authors (all still with Duke). This time, the team reached a very different conclusion.

“Short-term cannabis use in adolescence does not appear to cause IQ decline or impair executive functions, even when cannabis use reaches the level of dependence,”

the researchers reported in the February 2018 Addiction journal. “Family background factors explain why adolescent cannabis users perform worse on IQ and executive function tests.”

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Improved research methodology leads to new conclusions

The reasons for the reversal followed a change in how the research was carried out.

The 2012 research used data from the Dunedin Study, a longitudinal study that has been following 1,037 New Zealanders since their births in 1972 and 1973. For the follow-up, the research team utilized a longitudinal study tracking twins born in England and Wales. To this point, the twins have been tested at ages five, 12 and 18, and their data allowed the researchers to compare cannabis use and IQs at ages 12 and 18 in teens with very similar genetics. This made a big difference in the findings.

The findings suggest that biology, not cannabis, best explains the declines and impairments. The Meier-led team acknowledged that the new finding is consistent with what most researchers concluded in recent studies on cannabis use and neurocognitive performance.Many use cannabis to escape from pain.

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