Hi RDRK,
You have every reason to be concerned about lithium, but I will tell you that it is the main stabilizing agent that has been around since 1950. If it wasn't safe then the number of people on it would not be on it.
I have been on lithium for 15 years and the only occasional side effect I have had is a slight tremor in my hands, that is all. I did not gain weight. The only pain with lithium is that you have to have a lith level done fairly frequently until you become acclimated to the med.
If you would like to send me a private message to discuss further, please do. Don't be afraid, your doctors will not have you go cold turkey on the lamictal or seroquel without you being stabilized on the lithium.
By the way, the lithium has kept me from crashing down several times.
Please do talk to your therapist and doctor to discuss your apprehensions.
Everything will work out.
Slick