Little is known about the evidence to support prescription digital therapeutics, which are digital tools that rely primarily on software for diagnosis or treatment that have indications for use regulated by the Food and Drug Administration (FDA) and require a clinician's prescription. We conducted the first retrospective cross-sectional analysis of clinical studies of twenty prescription digital therapeutics authorized by the FDA and available on the market as of November 2022. Our analysis found that just two prescription digital therapeutics had been evaluated in at least one study that was randomized and blinded and that used other rigorous standards of evidence. Two-thirds of clinical studies of prescription digital therapeutics were conducted on a postmarket basis, with less rigorous standards of evidence than the standards used in premarket studies. More than half of studies did not report data on participants' race, and more than 80 percent did not report their ethnicity. More than one-third required English proficiency, and nearly half of nonpediatric studies had an upper age limit. These results suggest the need for a more rigorous and inclusive approach to clinical research supporting FDA-authorized prescription digital therapeutics. A stronger evidence base would increase confidence in these technologies' effectiveness and would enable more informed decision making about their clinical use and coverage.