One of Wall Street’s brightest stars of the last decade is taking it on the chin this year. John Paulson, the hedgie who famously earned about $4 billion in 2007 when he shorted the collapsing US housing market, has rung up losses of 22.3 percent through Sept. 30 in his merger fund, according to a report on Tuesday. A second Paulson & Co. fund, the advantage fund, which focuses on corporate events, is down 18.5 percent over the same period, the report said. Paulson’s weak performance, which was first reported by Bloomberg, is due in part to the firm’s holdings of scandal-ridden pharmaceutical companies such as Valeant Pharmaceuticals, Mallinckrodt, and Mylan. While Paulson’s funds are hurting, many are recovering. The S&P 500 gained 7.7 percent through Sept. 30 while event-driven hedge fund strategies are up 6.7 percent over the same period, according to data compiled by HFR. Reps from Paulson & Co. declined to comment.