Josie, Lithium does not always work, and serious side effects or lithium causing other health issues is not all that rare. If you consider regular blood testing for kidney function, thyroid function, and lithium serum levels easy to manage that's ok, but not everyone is going to feel that way. And not everyone is going to think those risks are worth the pro's. The side effects can be intolerable and persistant despite how well you take care of yourself. There is rumors and then there is people's real life experiences.

If someone feels the medication is no longer working why quiz them on why they stayed on it so long, why not find something else. Some medications may work for a time and then not, it's not a given that what once worked will always work. I think the op would know if it was still working well or not.