The FST showed a U-shaped curve on the response: after a certain point the antidepressant effect of these cannabinoid compounds appears to vanish. This is in keeping with the results of a 2007 study at McGill University using the synthetic cannabinoid WIN55,212-2. Says Dr. Gabriella Gobbi, who headed the study, "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."
This suggests depressed people should use cannabis with caution. The levels of various cannabinoids can vary widely among different batches: a dose that lightens the mood one day might, with a different strain, plunge you deeper into depression. But it also suggests an untapped new field of exploration for pharmacology. Dr. Gobbi is also doing research has begun on compounds like URB597, a drug which produces noticeable antidepressant effects by raising the levels of endogenous cannabinoids in the brain.