I just found a neat database (SIDER) from Peer Bork's group at EMBL: http://sideeffects.embl.de. This is a database one can query for drug indications and side effects. Using the data here, I find that there are 301 drugs with side effect or indication to alter body weight. Of those, 126 (41%) show both weight gain and decrease. This makes one wonder about genetic and environmental effects of those in the drug development trials. Therefore, there is a need to control things beforehand by partitioning based on genetics, if not also based on some lifestyle parameters.
The group's publication describing SIDER can be accessed here. The citation is Kuhn, et al. (2010) Molecular Systems Biology 6:343.