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As states increasingly legalize the use of marijuana, the debate surrounding its benefits vs. risks wages on. There is still much unknown about the effects of cannabis.
Thanks to the research of ASU assistant professor Madeline Meier, though, we are closer to understanding how marijuana affects three key things: IQ, physical health and socioeconomic mobility.
In 2012, Meier and colleagues published a report in the journal PNAS indicating that adolescents who use marijuana for many years show a drop in IQ from childhood to adulthood. This research has influenced public policy, particularly decisions to keep marijuana out of the hands of teens. Now in 2016, Meier answers the question of whether long-term marijuana users are in worse physical health. It turns out that they are not.
Her research published this month in the journal JAMA Psychiatry shows that aside from having bad teeth, marijuana users have few physical health problems at midlife. For example, marijuana users did not have worse lung function, higher levels of inflammation or worse metabolic health than non-users.
This latest finding comes on top of another paper published in Clinical Psychological Science in March, in which Meier and colleagues found that persistent cannabis use is associated with worse socioeconomic outcomes.
Study participants who reported using marijuana regularly (four or more days per week) showed a drop in social class compared with their parents. A standardized measure of social class was used, looking at things like a participant’s credit score, whether they relied on government assistance and the amount of debt they had.
The results were then controlled for potential alternative explanations. For example, one alternative explanation could have been that participants who reported regular use of marijuana showed a drop in social class not because of their marijuana use but because they had been incarcerated.
To test that possibility, the team members analyzed a subset of participants who had never been incarcerated. They found that even among that subset, a drop in social class was still observed among those who had regularly used marijuana.
“What this shows is that incarceration cannot explain marijuana users’ drop in social class,” said Meier.
On the flip side, Meier and her colleagues were also able to determine that participants who had never used marijuana actually ended up in a slightly higher social class than their parents.
Meier’s work on IQ, physical health and socioeconomic mobility was based on the same dataset of more than 1,000 New Zealanders followed from birth to age 38.
“We used the same sample, followed over the same time frame, and we found that marijuana is associated with adverse effects in some domains but not others,” said Meier.
Given her findings, Meier says we can’t label marijuana as “good” or “bad” for someone. It’s not that simple.
“It’s pretty clear that marijuana use increases risk for psychosis and can impair cognitive functioning, but marijuana use may not cause physical health problems, at least by midlife,” said Meier.