Cannabis has been used to treat depression for years. Many studies have concluded that Marijuana is indeed a cure for depression.
The University Medical Center Utrecht, in the Netherlands, has found that THC (which is found in cannabis) can alter the response to negative images or emotions.
Another study suggests that cannabis improves cognitive function in people suffering from bipolar disorder. Cannabis is a much faster working than other antidepressants. It also "stimulates the endocannabinoid system and speeds up the growth and development of nervous tissue" - (leafly.com)
As usual, unless marijuana is legalized further studies will be hindered and thus possible cures will only surface much, much later. We encourage you to do more reading on the subject before considering cannabis.