When placebo controlled trials are essential and equivalence trials are inadequate

Arguments against the use of placebo groups in clinical trials have been based on opinion rather than evidence. Ethical issues have been raised,1 but these are contentious. 2 3 Scientific requirements should not override ethical ones, but if placebo controls are not used, then active controlled trials (trials using other active drugs as controls) have to be able to determine the efficacy of an intervention and its likelihood of causing harm. #### Summary points We used the antiemetic ondansetron to explore the value of active controlled trials for two reasons. Firstly, the ethics of using placebo controls in ondansetron trials has been questioned repeatedly, both in oncology 4 5 and after surgery,6 causing confusion …