The main things to look out for are mood swings (especially if you're prone to mania or psychosis). The milder, more typical manifestation will be irritability, impatience and restlessness, to the point of (temporarily) changing your personality so you don't want to relax and socialize but only work.

Well, that and the potentially life-threatening skin conditions. Those are apparently rare, but I discontinued use when I saw some large purple blotches on my skin.