SAN DIEGO ( TheStreet) -- Japanese stock analysts are not hot for Arena Pharmaceuticals' ( ARNA) newly approved weight-loss pill Belviq. Eisai, the Japanese drug maker, is in charge of selling Belviq in the U.S. under terms of its partnership agreement with Arena. This is why the Japanese sell-side community is weighing in on Belviq's commercial prospects. Like their U.S. counterparts, Japanese analysts are skeptical that Belviq will become the blockbuster weight-loss pill envisioned by Arena and its shareholders. Here's what J.P. Morgan's Masayuki Onozuka told clients soon after Belviq was approved: "Commercial success hinges on stronger marketing: We expect only a limited profit contribution from lorcaserin Belviq , as (1) early-stage marketing will require caution while the drug’s safety is being confirmed; (2) Eisai has just 250 US MRs marketing representatives for primary-care drugs; and (3) we think the drug’s exceptionally mild effectiveness -- weight loss of less than 5% even after three months of use -- could prompt many patients to stop taking it. We forecast a sales contribution of $100 million in 2014 (year two) and $200 million in 2016. With Eisai’s PPI Aciphex set to go off-patent in the US in 2013, the company faces an environment unsuited to an aggressive sales push for primary-care drugs, and we will be interested in seeing what kind of marketing strategy it comes up with." Morgan Stanley MUFG analyst Mayo Mita wasn't any more effusive in her assessment of Belviq: "For the treatment of obesity, Belviq competes with Vivus' ( VVUS) Qnexa and Orexigen ( OREX)/ Takeda's Contrave. Of these three drugs, Qnexa has the highest efficacy but relatively high incidence of side effects. Belviq has the lowest efficacy, while Contrave achieves a balance between efficacy and side effects in our view… While not yet incorporated in our earnings models, assuming peak sales of $200-500mn million , we believe the impact to Eisai’s profits will be limited given that it will need to procure the product and incur costs for marketing/PMS studies." Credit Suisse's Fumiyoshi Sakal: "The approval comes as little surprise after an FDA advisory council recommended it by an 18:4 vote (one abstention) on 10 May and appears to be already reflected in Eisai’s share price, which is at a YTD high. While we are impressed with the approval -- the first in 13 years for a new obesity drug in the US -- we also expect it to be only a modest positive for the shares of Eisai. We also see little possibility of lorcaserin quickly developing into a blockbuster… Arena apparently regards Eisai as an optimal partner in selling lorcaserin, but it looks like Eisai will face substantial milestone payments and other costs.