In a study by researchers at the University of Saskatchewan, rats were given both short-term and longer-term (two-week) treatment with high doses of cannabinoids. The rats undergoing the longer treatment responded to tests in ways that indicated reduced anxiety. One such test involved depriving the rats of food for 48 hours. When food was reintroduced in an unfamiliar environment, the treated rats began eating much more quickly. The researchers note that this was not due to the appetite stimulation associated with marijuana, because the treated and untreated rats had similar eating patterns when they were given food in a familiar setting.

The study also found that treated rats showed less anxiety and spent less time immobile when undergoing stressful swimming and climbing tests, which the researchers interpreted as evidence of an anti-depressant effect. They point to the hippo-campus, the part of the brain where the neural growth occurred, which is important in regulation of mood disorders.

Dr. Xia Zhang, who led the study, cautions that these effects will still need to be examined in humans. If the results are the same, Zhang anticipates long-term clinical use of marijuana for anxiety and depression.