BackgroundIn this manuscript, we argue that within the context of phase IV, physician-researchers retain their fiduciary obligation to treat the patient-participants.DiscussionWe first clarify why the perspective that research ethics ought to be differentiated from clinical ethics is not applicable in phase IV, and therefore, why therapeutic orientation is most convivial in this phase. Next, assuming that ethics guidelines may be representative of common morality, we show that ethics guidelines see physician-researchers primarily as physicians and only secondarily as researchers. We then (...) elaborate on what a fiduciary obligation is and how some of the obligations are default duties. Lastly, we look at the fiduciary obligation of the physician-researcher in phase IV interventional trials.ConclusionThe fiduciary obligation to treat is not as easily waived as in earlier trials. Assuming the entwinement of research and practice in phase IV, physician-researchers, in collaboration with other researchers, investigators, and research ethics committees, should ensure that in terms of study design, methodology, and research practice, the therapeutic value of the research to the patient-participants is not diminished. (shrink)