An ethical dilemma arises in a clinical trial when the investigator(s) begin to believe that the treatment or intervention administered in one arm of the trial is significantly outperforming the other arms. A trial should begin with a null hypothesis, and there should exist no decisive evidence that the intervention or drug being tested will be superior to existing treatments or effective at all. As the trial progresses, the findings may provide sufficient evidence to convince the investigator of the intervention or drug’s efficacy. Once a certain threshold of evidence is passed, there is no longer genuine uncertainty about the most beneficial treatment, so there is an ethical imperative for the investigator to provide the superior intervention to all participants. Ethicists contest the location of this evidentiary threshold, with some suggesting that investigators should only continue the study until they are convinced that one of the treatments is better, and with others arguing that the study should continue until the evidence convinces the entire expert medical community.
The extent to which major research ethics policies endorse clinical equipoise varies. For instance, the Canadian Tri-Council Policy Statement endorses it; whereas, the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) does not. With regard to clinical equipoise in practice, there is evidence that industry-funded studies disproportionately favor the industry product, suggesting unfavorable conditions for clinical equipoise. In contrast, a series of studies of national cancer institute funded trials suggests an outcome pattern consistent with clinical equipoise.