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Study Says Marijuana Has Antidepressant Effect, but Only at Low Doses

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Updated June 30, 2014

A new study published in the October 24 issue of The Journal of Neuroscience says marijuana exhibits an antidepressant effect, but only at low doses. At higher doses, the opposite effect was observed, with serotonin levels dropping off even lower than the control group.

Dr. Gabriella Gobbi and colleagues, of McGill University and Le Centre de Recherche Fernand Seguin of Hôpital Louis-H. Lafontaine, injected rats with a synthetic cannabinoid and then subjected them to the Forced Swim Test, a test used to measure depression in animals. At the low dose, the cannabinoids produced an antidepressant effect in the rats accompanied by increased activity in the neurons that produce serotonin. Increasing the dose beyond a set point, however, reversed the effect and serotonin levels dropped, becoming even lower than the control animals that did not receive the drug.

Because of the difficulty in controlling the dose when marijuana is smoked, the authors say there are problems with using it directly as an antidepressant. "Excessive cannabis use in people with depression poses high risk of psychosis," said Dr. Gobbi in a press release. Instead, she and her team are focusing their research on a new class of drugs which would enhance the effects of the brain's natural endo-cannabinoids.

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