No weight gain here either (been on it for 2 months). In part, I think it's because I drink soooo much water now, which is really healthy. I read that part of Lithium weight gain is if people choose to drink sugary beverages, so when you are thirsty definitely go for water (caffeine isn't great either, it adds to the urge incontinence that some people suffer). Indeed, the extreme thirst (and subsequent need to urinate much more often) has been the worst/only side effect. It has helped a lot in the treatment of my depression (bipolar II).