I didn't lose until they put me on topamac but the p-doc who saw me most recently suspects that the lithium was starting to affect my thyroid in spite of the fact that the levels weren't showing much on the tests. He said even small changes can affect the weight in that way, and that is why excercize (I was doing 7 kilometers 4 times a week at one pont on the eclicycleand not losing) and diet control wasn't working. Normally you can keep it withing some bounds, but it is harder.