I gained 50 pounds in 8 weeks going on lithium 4 years ago. It suck because for a medication I mentally react well to it. But due to the weight gain I went off it. Took me until this year to lose the weight. About a year ago we were spinning tires trying to figure out what medication to us. The decision was to try a small dose of lithium. By small I mean 300 for months and over the last year I've gone up to 750mg. I was losing weight up until this last 150mg hike but I can also blame that on poor food choices.