I think some of the problem is the bipolar (or depression) itself. People who are depressed tend to eat more and exercise less. Also, people in a delicate state may be more easily influenced by what they read as side effects and therefore induce the side effects in themselves.

That being said, I gained 50 lbs while on lithium. Course I pretty much never left my bed and ate a lot of cookies (not that this had ever been a problem in the past). So perhaps certain medications do slow down your metabolism somewhat. Now I'm on seroquil and gabapentin and have been *very slowly* loosing weight.