What is the difference between negligence and failure to warn of a knowable risk?

The only situation plaintiff posits for her contention there is a meaningful difference between negligence and failure to warn of a knowable risk theories involves an extraordinarily hypothetical possible industry-wide practice of failing to disclose an unreasonably dangerous side effect of a drug. She argues that drug manufacturers could adopt an industry-wide practice of not advising of particular side effects. This she reasons would defeat a negligence claim. No doubt, an industry-wide practice may be admissible as evidence of whether a corporation or decisionmaker of ordinary prudence would act negligently in not advising as to the dangerous side effects of a drug. (Bullis v. Security Pac. Nat. Bank (1978) 21 Cal.3d 801, 809,

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