Research studies are very carefully designed and regulated.  Many, many steps in a patient visit are required that include careful evaluation of the pateint's disease as well as their general health.  Nothing can be missed and each patient visit is reviewed by external personnel (while maintaining their privacy) for accuracy and completeness.  This is well beyond what is done in day-to-day clinical medicine.  Thus the quality of care you will receive in a clinical research study far exceeds what you may receive elsewhere.