The study, conducted by a group led from University College London, in the United Kingdom, investigated the “impact of adolescent cannabis use on intellectual and educational outcomes” by following a group of 2,235 children born in the Bristol area.
Researchers tested the children’s IQs at age eight and again at 15, by which time 24 per cent of the group have reported using cannabis at least once and just over three per cent had used cannabis at least 50 times.
While the group “found that cannabis users had lower teenage IQ scores and poorer educational performance than teenagers who had never used cannabis” these results were mixed with the same children experiencing higher rates of behavioural problems, depression or other substance abuse issues.
After adjusting for these other issues, the study showed that teenaged cannabis use did not influence poorer mental or educational performance.
“These findings therefore suggest that cannabis use at the modest levels used by this sample of teenagers is not by itself causally related to cognitive impairment,” the study read. “Instead, our findings imply that previously reported associations between adolescent cannabis use and poorer intellectual and educational outcomes may be confounded to a significant degree by related factors.”
Lead researcher Claire Mokrysz said, in relation to a previous, but related, study, that a correlation between adolescent cannabis use and decreased intelligence should not be seen as causation.
“People often believe that using cannabis can be very damaging to intellectual ability in the long-term, but it is extremely difficult to separate the direct effects of cannabis from other potential explanations,” Mokrysz said in 2014. “It’s hard to know what causes what — do kids do badly at school because they are smoking weed, or do they smoke weed because they’re doing badly? This study suggests it is not as simple as saying cannabis is the problem.”
The Canadian Liberals, promising to legalize cannabis, have said their priority is keeping the plant away from youth in the country.
“There needs to be reasonable restrictions on making sure that we keep it away from kids, because I think that is very much in the public interest,” Bill Blair, the government’s lead on regulation said recently. “We also have to ensure that the social and the health harms are properly managed and mitigated, and that can be done through regulation.”