Document Type

Article

Publication Date

5-2026

Abstract

Market share liability, which permits allocating proportional responsibility to each tortious member of an industry when victims cannot identify the exact source of their injurious exposure, enjoyed its judicial heyday in the 1980s. It originated in the peculiar setting of litigation over a distinctive cancer that developed decades after in utero exposure to the drug diethylstilbestrol (“DES”), which a few hundred companies had produced and sold for the prevention of miscarriages before federal regulators withdrew it from the marketplace. Although judges have occasionally attempted novel extensions of this theory to other products, and academic commentators remain fascinated by its use, market share liability has faded from the scene. In the meantime, a strange new variant emerged, and it could have far greater reach than market share liability, though so far it has flown mostly below the radar of the torts cognoscenti. In contrast to market share, it visits full responsibility on the manufacturer of a brand-name drug for patient injuries unmistakably caused by generic versions sold by its competitors. This Article denominates the newer approach as “market shift liability” and documents its gradual spread while critiquing the doctrine on a number of different grounds.

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