It is tremendous task starting from planning and implementing, to analyzing and writing down a RCT. I have also come across single authorship RCT. In one case I sure knew that many people were involved in the particular RCT and rightful authors, but they were not given there due. I wonder whether single authors have different definition of authorship than conventionally held or as ethical guidelines suggest. As a reviewer I will be very cautious with RCT manuscript with single authorship.