I don't know about the science behind it, but as a teenager and young adult I had numerous episodes in and out of mental institutions and was diagnosed by various professionals as bipolar, schizophrenic, or borderline personality disorder. I tried several antidepressants and "mood stabilizers" some of which never worked and some that worked but with side effects I couldn't accept. During this period of my life I was definitely occasionally a danger to myself and others.

About 10 years ago, as an adult never having tried any illicit substances, I started using cannabis and found marked improvement in my mood and focus. Since then, smoking weed every few days, I have had zero "episodes", I am happy most of the time, am in a stable long-term relationship with a new child and am generally a productive member of society.

I have tried to research scientific studies that explain these results but have always found the corpus lacking. I think these interactions definitely deserve more exploration.