Lithium was used by the Roman and Greeks, so it has been in the pharmeceutica for thousands of years. It flows out of the ground in some natual springs.
The trouble with lithium is maintaining a blood level. Most of the articles I've read say blood tests are needed from time to time, to be SURE it's staying at the right amount in the person's system. It's called Therapeutic Drug Monitoring. The dose has to be adjusted from time to time to respond to changes in health, prescriptions, etc.
And people have to be VERY careful of what over the counter drugs and herbals they take!!!!!!
Dehydration, other medications and other illnesses, can interfere with lithium doing its job. Even some ordinary blood pressure meds will interfere with lithium. And then some kidney diseases mean people need a lowered dose of lithium.
Motrin, Aleve and a host of other fairly ordinary drugs can interact with Lithium, requiring a lower (or higher) dose of lithium to get the blood level of lithium to be correct. I don't think most people realize how simple it is to 'mess up' one's lithium levels.
I've read a number of cases over the years, of people 'going off' while taking lithium - in all cases, their blood levels of lithium were not at a therapeutic dose. In other words, they weren't getting enough to have it - do anything at all for them - for various reasons.