Several large hedge fund investors bought more shares in beleaguered drug giant Valeant Pharmaceutials — just as its shares began to tumble.

Steve Mandel’s Lone Pine, with a 2.2 percent stake in Valeant, bought 2.2 million more shares in the third quarter for a 7.5 million-share position, it revealed in a securities filing Monday.

Andreas Halvorsen’s Viking Global bought 376,615 shares, giving it 4.9 million shares, a 1.5 percent stake.

Ruane Cunniff bought 2 million shares on Oct. 31, giving it a 11.5 percent stake.

John Paulson trimmed his stake, selling 110,000 shares, but still has a 8.9 million stake.

Valeant shares dipped 20 percent in the third quarter — and are down 59 percent so far in the fourth quarter. Shares fell 2.8 percent on Monday, to close at $73.32.