The number needed to treat (NNT) statistic was developed to facilitate thepractice of evidence-based medicine. Placebo was assumed to betherapeutically inert when the NNT was originally conceived, but more recentdata for conditions such as major depressive disorder (MDD) suggest that theplacebo control condition can have considerable therapeutic effects.Complications arise because the NNT calculated from randomised controlledtrials (RCTs) reflects a comparison between medication plus clinicalmanagement and placebo plus clinical management, whereas, in the clinicalsetting, physicians choose between prescribing open medication, observing apatient over time with a supportive approach, and doing nothing. Thus, NNTsderived from clinical trials are not directly relevant to clinicaldecision-making, because they are based on control conditions that do notexist in standard practice. Additional difficulties may arise when usingNNTs to compare alternative treatments for MDD, such as medication andpsychotherapy, since these comparisons require the control conditions uponwhich the respective NNTs are based to be similar. Whereas pill placeboconditions include intensive clinical management and elicit expectations ofimprovement, attention control conditions for psychotherapy research areless well developed. Often the effects of psychotherapy are gauged against await-list control condition, which has substantially fewer therapeuticcomponents than a pill placebo control condition. To improve the clinicalutility of NNTs for the treatment of MDD, we advocate effectiveness studiesthat include treatment conditions resembling actual clinical practice,rather than using placebo-controlled RCTs for this purpose. Until suchstudies are performed, the effect of bias in comparing NNTs acrosstreatments can be controlled by ensuring that the RCT control conditionsupon which the NNTs are based are comparable.