It's funny because I kind of know a lot about Lithium as they put me on it when I tried to kill myself at age 19.
It basically calms those areas of your brain that would make you manic/anxious and increases the serotonin in your brain, the pleasure chemical....so it makes you feel happier, less anxious, and therefore less likely to kill yourself (in my case)...I stayed on it for about 4 months...and although I cannot say for sure that it was the Lithium that stabilized me, I'm sure it didn't hurt the situation.
It was actually discovered for medical use in a prison, I wanna say without looking it up on Wikipedia that it was around the early 1900 but maybe it was the 1940s? Anyhow, they had a huge difference in the amount of violence with the prisoners when held to a national average. Upon further investigation they discovered there were high amounts of Lithium naturally occurring in the water as it is an element but can be dissolved in water as a metallic-salt. And viola...you have the drug we have today.
It did give me some strange side-effects...I would get strange muscle twitches, mostly in my back that would cause me to twist/twitch in a funny way....it was tolerable though probably funny looking at times, lololol.