Modern health care relies extensively on the use of technologies for assessing and treating patients, so it is important to be certain that health care technologies (i.e., pharmaceuticals, devices, procedures, and organizational systems) perform their professed functions in an effective and safe manner. Philosophers of technology have developed methods to assign and evaluate the functions of technological products, the major elements of which are described in the ICE theory. This paper questions whether the standard of evidence advocated by the ICE theory is adequate for ascribing and assessing technologies employed in health care. The paper proposes that the general problem with the standard of evidence embodied in the ICE theory (i.e., testimony and evidence of mechanisms) is too permissive for assessing medical technologies, in that it does not take into account the relative benefit and harm of medical technologies in ensuring safe functional performance in patients. The paper illustrates how evidence-based medicine (EBM) has demonstrated the value of clinical research methods, including observational studies, randomized and non-randomized clinical trials, and formal techniques, such as meta-analysis, to measure therapeutic effectiveness. I argue, therefore, that evidence from clinical research studies should take precedence over the testimonial evidence and other types of non-clinical evidence, in providing justification for health technologies.