In some cases, a simpler explanation for the link between marijuana and psychosis
PROBLEM: When we first figured out that there's a solid association between mental illness and marijuana use in adolescents, the most common, if panicked assumption was that smoking pot must mess with teens' developing brains, in some cases actually causing psychosis. Although evidence does not exist to prove that conclusively, other studies have found that marijuana is at least associated with an increased risk of developing a psychiatric disorder. But what if we're thinking about this backwards, and people with psychosis are just more likely to smoke pot?
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METHODOLOGY: Researchers in the Netherlands surveyed over 2,000 Dutch teens about their pot smoking habits throughout adolescence. They then asked them questions -- like, "Do you ever see things that others do not?" -- meant to identify "thought," "social," and "attention" problems, and determined whether these symptoms appeared before or after they began using marijuana. A family history of mental illness, along with alcohol and tobacco use, was factored in to the analysis.
RESULTS: Among the 44 percent of teens who admitted to smoking pot, use of the drug at age 16 was linked to the development of psychotic symptoms at age 19. But the researchers also found that where kids began to display signs of psychosis at an early age, they then tended to start using marijuana in their later teens -- for them, the psychosis came before the drug use.
CONCLUSION: The association between psychosis and marijuana use is not one of clear cause and effect -- it appears to run in both directions. While smoking pot was indeed linked to an increased risk of psychosis, initially having psychotic symptoms was also associated with an increased likelihood of later marijuana use.
IMPLICATIONS: As with previous studies, the researchers weren't able to establish that marijuana use is directly causing an increased risk of psychosis, or vice versa. Their point is that since some teens with psychotic symptoms seem more likely to self-medicate with marijuana, it could be confounding the data that suggests pot somehow causes psychosis. Medical marijuana, it should of course be noted, is not intended to treat mental illness, and its full range of effects on developing brains remains poorly understood.
The full study, "Cannabis Use and Vulnerability for Psychosis in Early Adolescence - a TRIALS Study," is published in the journal Addiction.