While Arena Pharmaceuticals (ARNA) and VIVUS (VVUS), makers of the obesity drugs Belviq and Qsymia, respectively, both garner a lot of attention on Fool.com, they also have attracted the attention of the short sellers. In this video, Motley Fool health-care analyst David Williamson talks about the "buy the run-up, short the launch" trend, and whether the short-sellers are right not to believe in these stocks.