Over the years, Dr. Elizabeth Osuch, a researcher in Canada studying mood and anxiety disorders and the impact of marijuana, has seen "many youth" smoke pot "heavily." And despite previous research suggesting those who start at a young age are at a higher risk of psychiatric issues and cognitive dysfunction, many young people still "believe it improves their psychiatric conditions because it makes them feel better momentarily," she says in a Science Daily news release. So she set out to look at the relationship between early marijuana use and psychiatric and cognitive function and found that early marijuana use is linked to lower IQ as well as brain function anomalies, and that there is no evidence marijuana use eases depression.
To test this, Osuch placed 74 youth in four groups: a control group who didn't use pot and didn't have depression, marijuana users with depression, marijuana users without depression, and non-users with depression. Reporting in the journal Acta Psychiatrica Scandinavica, she notes that regular smokers who started when they were younger than 17 had abnormal brain function in areas linked to memory, self-referential activity, reward processing, and visuo-spatial processing. Starting to use pot before 17 was also linked to a lower IQ. Of course, 74 is a small sample size, and she calls on larger studies to investigate further. She also found a higher rate of a genetic variation of a gene involved in brain development and memory among early smokers—a "novel finding that suggests this genetic variation may predispose youth to early marijuana use." (Regular pot use has been linked to lower BMI.)