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Study Finds No Causal Link Between Marijuana Use And Depression
NORML | 09/28/2006

Baltimore, MD: Marijuana use by adults is not a statistically significant predictor of depression, according to the results of an ongoing longitudinal study to be published in the October issue of the journal Addiction.

Investigators at John Hopkins University in Baltimore and at the Bloomberg School of Public Health in Santa Monica assessed the association between self-reported marijuana use and current depression in 8,759 adults (age range 29-37 years) over a 17-year period. Investigators concluded, "After adjusting carefully for baseline differences between adults who subsequently use marijuana and those who abstain, the significant associations that are initially present between ongoing marijuana use and depression are substantially reduced, if not eliminated."

They added, "The findings reported in this paper suggest that the associations observed between marijuana use and subsequent depression status may be attributable not to continued marijuana use, per se, but to third (common) factors associated with both the decision to use marijuana and to depression."

A separate study co-authored by NORML Advisory Board Member Dr. Mitch Earleywine and published last year in the journal Addictive Behaviors determined that adults who use cannabis report suffering from less severe incidents and/or symptoms of depression than non-users.

"Despite comparable ranges of scores on all depression subscales, those [respondents] who used cannabis once per week or less had less depressed mood, more positive affect, and fewer somatic (physical) complaints than non-users," authors wrote. "These data suggest that adults apparently do not increase their risk for depression by using marijuana."

Commenting on the most recent study, Earleywine said, "This new data is actually markedly stronger than my earlier work because the investigators utilized a large, representative sample and conducted long-term follow up research. If marijuana use caused depression, this design model would have revealed it by showing the development of symptoms in users. There's simply no support for the idea."

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