Washington, Oct 24 : A study has found that cannabis works effectively as an anti-depressant when taken in low doses, but worsens depression when taken at higher doses.

The neurobiological study, led by Dr. Gabriella Gobbi of McGill University and Le Centre de Recherche Fernand Seguin of Hôpital Louis-H. Lafontaine affiliated with l'Université de Montreal has found that a synthetic form of THC, the active ingredient in cannabis, is an effective anti-depressant at low doses, however, when taken in higher doses, the effect reverses itself and it worsens depression and other psychiatric conditions like psychosis.

It has been known that because of the depletion of the neurotransmitter serotonin in the brain depression occurs and so the SSRI-class anti-depressants like Prozac and Celexa work by enhancing the available concentration of serotonin in the brain to stop the condition.

This study offers the first evidence that cannabis can also increase serotonin, at least at lower doses.

In the study, laboratory animals were injected with the synthetic cannabinoid WIN55, 212-2 and then tested with the Forced Swim test – a test for measuring ‘depression’ in animals.

Dr. Gobbi said that from the analyses it was found that an antidepressant effect of cannabinoids paralleled by an increased activity in the neurons that produce serotonin. However, increasing the cannabinoid dose beyond a set point completely undid the benefits.

"Low doses had a potent anti-depressant effect, but when we increased the dose, the serotonin in the rats' brains actually dropped below the level of those in the control group. So we actually demonstrated a double effect: At low doses it increases serotonin, but at higher doses the effect is devastating, completely reversed,” Dr. Gobbi said.

She explained that the anti-depressant and intoxicating effects of cannabis were due to its chemical similarity to natural substances in the brain known as ‘endo-cannabinoids,’ which were released under conditions of high stress or pain. They interact with the brain through structures called cannabinoid CB1 receptors.

In the study it was demonstrated that the receptors had a direct effect on the cells producing serotonin, which was a neurotransmitter that regulated the mood.

"As a psychiatrist, I noticed that several of my patients suffering from depression used to smoke cannabis,” Dr. Gobbi said.

“And in the scientific literature, we had some evidence that people treated with cannabis for multiple sclerosis or AIDS showed a big improvement in mood disorders. But there were no laboratory studies demonstrating the anti-depressant mechanism of action of cannabis,” she added.

When it is smoked in the form of marijuana joints, controlling the dosage of natural cannabis is difficult. So, there are many hurdles for using it directly as an anti-depressant.

"Excessive cannabis use in people with depression poses high risk of psychosis," Dr. Gobbi said.

The study is published in The Journal of Neuroscience. (ANI)