The other less clear downside catalyst may have been profit-taking in July. Between May 1st and July 5th, Achillion's stock increased in value by 46% without much in the way of news, other than some sparse analyst commentary. It's possible given the uncertain nature of the company's pipeline that investors decided to lock in their gains. Since November, any rallies in Achillion's stock have been met with selling pressure within a matter of weeks, and that looks to be the case again with its performance in July.