Pot and Depression: Mixed Findings

Oct. 25, 2007 -- New research on marijuana and depression suggests that THC, pot's key chemical, may help or hurt depression depending on the dose.

That news appears in The Journal of Neuroscience.

Canadian researchers tested a synthetic cannabinoid (the class of chemicals that includes THC) in lab tests on rats.

The rats spent five minutes in a container of water. They swam and tried to get out of the water, but when they didn't succeed, they gave up, which the researchers read as a sign of despair. (The rats were then rescued by the researchers.)

In previous studies, rats have resisted despair longer when given antidepressants before the swim test, according to the researchers.

In this study, before being placed in the water, the scientists injected high or low doses of a synthetic cannabinoid into some of the rats. For comparison, the scientists gave other rats saltwater shots.

The rats that got low doses of the synthetic cannabinoid swam longer than the other rats. The rats that gave up the fastest were those that got the high dose of the synthetic cannabinoid.

Further tests showed that the rats made more of the antidepressant brain chemical serotonin after getting the low dose of the synthetic cannabinoid. But serotonin production sank below normal levels with the high dose of the synthetic cannabinoid.

Synthetic cannabinoids might make good antidepressants, but the challenge is to get the cannabinoid dose right for depression without triggering other problems, note the researchers.

They included Gabriella Gobbi, MD, PhD, of Montreal's McGill University.

Gobbi and colleagues aren't recommending marijuana for depression. "Excessive cannabis use in people with depression poses high risk of psychosis," Gobbi says in a news release.