In psychiatry, comparative analyses of therapeutic options and the aggregation of data from clinical trials across different therapeutic approaches play an important role in clinical decision making, treatment guidelines, and health policy. This approach assumes that trials of pharmacological and behavioural therapies generally produce the same level of evidence when properly designed. However, trial design for behavioural interventions has some unique characteristics and control groups vary widely, which influence the effects observed in any given trial. In this Personal View, we review various control conditions typically used in psychiatry, outline their effect on the internal validity and expected effect size of a trial, and propose a decision framework for choosing a control condition depending on the risk to the patient population and the stage of development of the therapeutic intervention. We argue that the choice of control group and its justification need to be taken into consideration when comparing behavioural and pharmacological therapies.
