The effects of distant, intercessory prayer on health outcomes have been studied in a range of randomised, blinded clinical trials. However, while seeking the evidentiary status accorded this ‘gold standard’ methodology, many prayer studies fall short of the requirements of the World Medical Association's Declaration of Helsinki for the ethical conduct of trials involving human subjects. Within a sample of 15 such studies published in the medical literature, many were found to have ignored or waived key ethical precepts, including adequate (...) standards of care, patient confidentiality and informed consent. Prayer was considered in most studies to pose negligible or no risk to subjects, despite the fact that no clear mechanism of action nor any safety monitoring procedures were described. As a result, many studies did not meet basic ethical standards required of clinical trials of biophysical interventions, making application of their results ethically problematic. If investigators wish their data to adequately inform the use or rejection of intercessory prayer to improve health, these shortcomings should be addressed in future studies. (shrink)