Lithium is like two different medications: low doses are pretty easy to manage and produce few side effects. High doses are tricky to manage, require close monitoring to stay safe, and can cause side effects which make people want to consider alternative treatments. Weight gain can occur with lithium. At first almost everyone will gain a few pounds as their body hangs on to more water (salt effect). Some people can continue to gain weight, though. This is much less of a problem with lithium than with valproate, both in how often it happens and how much weight is gained. Usually at this point we will switch medications, but some people can control the weight issue with regular exercise, wise eating, and avoiding alcohol entirely -- all good health habits anyway.