Brattle economists have worked on a number of cases in which branded drugs have been faced with patent challenges by generic companies under the Hatch-Waxman Act. In many of these cases, the generic company has sought to enter the market “at risk”—i.e., prior to resolution of the patent suit—and the branded drug company has responded with a request for a preliminary injunction. In these injunction cases, we have been asked to evaluate whether the branded drug company would suffer irreparable harm due to “at risk” generic entry. We have addressed this question by analyzing the likely impact of such entry on the branded drug company’s sales, research incentives, marketing efforts, employment, and manufacturing facilities. We have also investigated the impact of such entry on the branded drug’s formulary status and the goodwill of its customers.