California Code, Health and Safety Code - HSC § 110025

(a) “Substantial evidence” means evidence consisting of adequate and well-controlled investigations, including clinical investigations, by experts qualified by scientific training and experience to evaluate the effectiveness of the drug or device involved, on the basis that it could be fairly and responsibly concluded by the experts that the drug or device will have the effect it purports or is represented to have under the conditions of use prescribed, recommended, or suggested in the labeling, proposed labeling, or advertising of any drug or device.

(b) If the department determines, based on relevant science, that data from one adequate and well-controlled clinical investigation, and confirming evidence, obtained prior to or after the investigation, sufficiently establish effectiveness, then the department may consider that data and evidence, to constitute substantial evidence for purposes of the preceding sentence.