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Frequent cannabis use by teens linked to drop in IQ

19 March 2021

Adolescents who regularly use cannabis may experience a decline in IQ over time, a study in Psychological Medicine has found.

The researchers observed a drop of approximately two IQ points in young people who frequently used cannabis (at least weekly for a minimum of six months and/or had more than 25 reported lifetime uses and/ or a diagnosis of cannabis dependency) compared to those who didn’t/rarely used it (less than five times).

Further analysis suggested the IQ decline was mainly related to a reduction in verbal IQ.

The research looked at seven longitudinal studies of 808 young people with frequent or dependent cannabis use, and 5308 controls.

Senior author Professor Mary Cannon said: ‘Loss of IQ points early in life could have significant effects on performance in school and college and later employment prospects.’

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