I can't remember exactly what chemical in many creatine products was causing depression (I think 1,3-diethylamine), but I myself actually had a bout of mild depression from using creatine while seeing mediocre results at best (maybe due to lack of ambition to work out in the first place due to the depression). I know some creatines don't have this chemical in them.
Does anyone know for sure what the chemical is? And of brands that don't contain it?