Basically, before the war on drugs, a lot of interesting research was being done in psychiatry around different psychoactive drugs (including cannabis). Ecstasy, for example, shows some usefulness in treating shell-shock. LSD shows some evidence of helping with PTSD.
Since the war on drugs, however, the research has been lacking (as I’m sure you’re aware). This article is evidence that the scientific community is slowly warming back up to more research on the subject, and hopefully to examining cannabis’ uses in treating mental conditions.