The study, led by Daniele Piomelli, the Louise Turner Arnold Chair in Neurosciences and director of the Centre for Drug Discovery at the University of California, Irvine, a drug called URB597, created by the researchers, which blocked anandamide degradation in the brain, thereby increasing the levels of this chemical.
URB597 works by inhibiting FAAH, an enzyme in the body that breaks down anandamide.
Dubbed "the bliss molecule" for its similarities to the active ingredient in marijuana, anandamide is a neurotransmitter that is part of the brain's endocannabinoid system and it has been shown to play analgesic, anti-anxiety and antidepressant roles.
In the study, the researchers administered URB597 to chronically stressed rats, which showed behaviours similar to those seen in depressed human patients.
After five weeks of treatment, the stressed rats treated with the drug were behaving similarly to a comparison group of unstressed animals.
Piomelli said that the marijuana could be utilized for treatment of depression.
"These findings raise the hope that the mood-elevating properties of marijuana can be harnessed to treat depression," Piomelli said.
"Marijuana itself has shown no clinical use for depression. However, specific drugs that amplify the actions of natural marijuana-like transmitters in the brain are showing great promise," he added.
The study will be published in Biological Psychiatry.