We can't say a whole lot about it because we're involved in the litigation, but anybody defending a prescription drug product liability case where the plaintiff was prescribed more than one drug concurrently should take a look at the warning causation reasoning in Simon v. Wyeth Pharmaceuticals, Inc., 2010 WL 2243661 (Pa. C.P. Phila. Co. May 5, 2010). The court found an inconsistent verdict where the same prescriber had jointly prescribed two different drugs, but the jury found only one manufacturer's labeling inadequate as to the same risk. The finding that one label was adequate meant that the prescriber, when the prescription was made, had received an adequate warning about that risk. That necessarily defeated causation as to every defendant, because - regardless of the source of the warning - the prescriber had gone ahead after having been adequately warned.
Causation thus makes a multi-drug regimen failure-to-warn case an all or nothing proposition. If any of the defendants' warnings is adequate as to the risk at issue, then all defendants win, because that means the prescriber acted after having been adequately warned. Make sure the jury instructions are phrased accordingly.