In Sindell v. Abbott Laboratories (1980) 26 Cal. 3d 588, the California Supreme Court recognized the theory of market share liability. The plaintiff alleged injury in utero caused by the drug diethylstilbestrol. Plaintiff's mother had taken diethylstilbesterol (DES) during pregnancy and the court acknowledged it would be impossible for her to identify which manufacturer had produced the drug she ingested. The court nevertheless permitted an action, provided that a substantial percentage of DES manufacturers were joined, and that the liability of any one defendant would be limited to the same proportion that their production of the drug bore to the entire market. Sindell, 26 Cal. 3d 588, 163 Cal. Rptr. 132, 607 P.2d 924, 937. The California Supreme Court determined whether a complaint stated a cause of action under the Restatement's "concert of action" doctrine, and explained these principles by quoting Dean Prosser's comment that "'those who, in pursuance of a common plan or design to commit a tortious act, actively take part in it, or further it by cooperation or request, or who lend aid or encouragement to the wrongdoer, or ratify and adopt his acts done for their benefit, are equally liable with him. Express agreement is not necessary, and all that is required is that there be a tacit understanding ... ." (Sindell, at p. 604, quoting Prosser, Law of Torts (4th ed. 1971) 46, p. 292.)