A better measure of Eisai's prowess here is Halaven, a treatment for late-stage breast cancer that the company markets independently. Despite Eisai's oncology focus and management's projections of "blockbuster" sales, Halaven generates less than $300 million in annualized revenue two years post launch. That's hardly the hallmark of a U.S. drug -marketing powerhouse. 4. Arena only receives roughly one-third of Belviq's profits. Although valuation metrics are often ignored in the early stages of a drug launch, the likelihood that Belviq stumbles out of the gate may make investors more valuation sensitive with respect to Arena. Based on script data thus far, I estimate Vivus' Qsymia will generate below-consensus sales of only $200 million in 2013. It might not even do that well. I would be surprised if peak U.S. sales for Qsymia exceeded $650 million. (Although the stock has declined meaningfully as investors have lowered expectations for Qsymia, Vivus is still probably a decent short at current prices.) Arena and Eisai's 190 sales representatives that will launch Belviq is too small a group to adequately cover the general practitioner market. But let's give them the benefit of the doubt and assume these sales reps do a surprisingly (if not unbelievably) effective job scrounging up $750 million in Belviq sales in 2015. For Arena, that would generate $250 million in revenue. Applying a five times multiple to these near-peak revenues suggests the present value of Belviq by the end of next year is only $996 million. The math is clear: Even though Arena shares have tumbled over the past few months, plenty of downside remains. Arena is still a good short. Sadeghi has no positions in stocks mentioned in this column.