No weight gain (other than from aging and alcohol) in 25 years of use. I have started to have a little tremmor in my hands but it may be nerves cause it goes away. Here is my worst side effect, dry mouth which can cause, you guessed it, bad breath. Bummer. Maybe this is not a problem for everyone. But I have to be vigilant at drinking fluids, taking mints etc to manage this. Kind of embarassing, but this is not an uncommon problem for anyone having to take medications. Then again, I would be in the hospital without lithium.