Lithium is a strange drug. It also cures bipolar disorder and nobody knows why. It also fucks up the liver over time and basically people on lithium eventually have to make a choice between dying or being insane.
It's mostly the kidneys that get damaged, not so much the liver. It also has a massive amount of benign or merely annoying side effects. Lithium might even be the drug with the largest overall amount of side effects. It's certainly a weird one. High-dose lithium is extremely hard on your kidneys and may well lead to kidney failure in a decade or so. Medium-dose lithium is a lot more gentle but still requires monitori…
As a matter of fact, lithium patients aren't much worse off when it comes to kidney function. Especially with modern levels of around 0.6 to 0.8 mmols.
Lithium has many modes of action, ion channels like you said, but also GSK3 function, BDNF changes and many more. It even changes the DNA methylation.