ClinicalTrials.gov, stem cells and 'pay-to-participate' clinical studies. 
Numerous US businesses that engage in direct-to-consumer advertising of stem cell interventions that are not US FDA-approved also recruit clients by listing 'pay-to-participate' studies listed on ClinicalTrials.gov .  Individuals considering enrolling in such studies and NIH officials responsible for overseeing the database need to be aware that some businesses are using the registry to promote unapproved stem cell interventions that study subjects are charged to receive.  Inclusion of such studies in ClinicalTrials.gov reveals that the database needs better screening tools.  In particular, screening should evaluate whether studies submitted to the registry have been reviewed and permitted to proceed by the FDA in the case of clinical studies requiring FDA clearance in addition to institutional review board approval.