Despite investigations into the composition of its key drug, Acthar gel, as well as into its marketing practices, Questcor Pharmaceuticals (NASDAQ: QCOR) has announced that it is being bought by Mallinckrodt (NYSE:MNK) for $5.6 billion. Short-sellers have been attacking Questcor relentlessly recently, alleging that the stock could, in fact, be worth nothing if Acthar's composition is found not to be what the company claims.

In this video, Motley Fool health-care analyst David Williamson looks at the purchase, which was at a 27% premium to the stock's price, and discusses the pros and cons for Mallinckrodt. He also tells Questcor bulls everywhere that this signals the end of the battle for Questcor investors, and that they've officially won the fight on this stock over the bears.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.