The researchers used data on 2235 children – mapping tobacco and cannabis use against IQ at age 15 and educational performance at age 16.
Writing in Journal of Psycopharmacology, the researchers say, ‘There is much debate about the impact of adolescent cannabis use on intellectual and educational outcomes.
‘We investigated associations between adolescent cannabis use and IQ and educational attainment in a sample of 2235 teenagers from the Avon Longitudinal Study of Parents and Children.
‘After full adjustment, those who had used cannabis 50 times did not differ from never-users on either IQ or educational performance.
The scientists say that there is a ‘robust’ link between smoking cigarettes and lower achievement in education – even when cannabis is excluded.
The researchers write, ‘Adjusting for group differences in cigarette smoking dramatically attenuated the associations between cannabis use and both outcomes, and further analyses demonstrated robust associations between cigarette use and educational outcomes, even with cannabis users excluded.
‘These findings suggest that adolescent cannabis use is not associated with IQ or educational performance once adjustment is made for potential confounds, in particular adolescent cigarette use.
‘Modest cannabis use in teenagers may have less cognitive impact than epidemiological surveys have previously suggested.’