Before any individual case matters, plaintiffs must show the product is capable of causing the disease — through epidemiology, toxicology, and expert testimony that survives the Daubert reliability test. Only then does specific causation (your dose, your timeline, your alternative risk factors) come into play.
When general causation fails, everything fails: the Zantac MDL court's 2022 exclusion of plaintiffs' general-causation experts effectively ended roughly 50,000 federal claims at once. When it holds, it holds for everyone — which is why both sides spend millions on this single question.
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