Not every stock that falls on tough times is worth buying in portfolios, but sometimes, catalysts can spark shareholder-friendly rallies, and in those situations, it can make sense. For example, risk-tolerant investors might want to consider picking up shares in the beaten-up biotech stocks Zogenix (NASDAQ: ZGNX), Insys Therapeutics (NASDAQ: INSY), and Keryx Pharmaceuticals (NASDAQ: KERX). All three of these stocks are former highfliers, and each has catalysts that could help them regain some of their former glory.