40 pound weight gain over a period of 3 months was the side effect of lithium for me. It is a medication I will not be taking again. Glad I did not stay on it longer now that I know that it also could have harmed my teeth.
There are so many other medications out there that can be tried there is no reason to stick with one that either is not working or is giving us side effects we can not tolerate. I am sure it is a wonder drug for some people though. It just isn't the right medication for me. Not sure what is though as I have been through many of them and still seeking the right ones after 10 years of trying.