Piper Jaffray analyst David Amsellem says his firm's survey of 39 physicians is a "mixed bag" for Allergan's (AGN) Linzess. The feedback from doctors suggest that the prospects for double-digit annual volume growth for Linzess over the long-term "are not nearly as strong as sentiment in the broader investor community would suggest," Amsellem tells investors in a research note. A bulk of the respondents have a favorable view of Linzess but also "misgivings regarding the incidence of diarrhea," the analyst adds. Further, Amsellem does not conclude that Synergy Pharmaceuticals' (SGYP) recently approved Trulance in chronic idiopathic constipation is the "poor man's Lizness." The lower incidence of diarrhea associated with Trulance does not necessarily mean that it is a less potent agent, the analyst contends. He keeps a Neutral rating on Allergan with a $205 price target.