Background. Placebo response, drug response, and drug–placebo differences appear to vary among psychiatric conditions.
Method. We evaluated the Food and Drug Administration (FDA) Summary Basis of Approval (SBA) reports to compare the magnitude of placebo response, magnitude of psychotopic drug response, and drug–placebo differences among various diagnostic groups such as depression, anxiety, and psychotic disorders.
Results. Six diagnostic groups (psychosis, obsessive–compulsive disorder (OCD), generalized anxiety disorder (GAD), depression, post-traumatic stress disorder, panic) varied in response to both placebo and active drug treatments. Response to placebo was high among patients participating in GAD, depression, and panic disorder clinical trials. Conversely, patients participating in psychotic disorder and OCD trials experienced low response to placebo.
Conclusion. Our findings indicate that the magnitude of placebo response and drug response were heterogeneous and were statistically significantly different among various psychiatric disorders. Although a noticeable degree of heterogeneity was detected in the drug–placebo ratio among various disorders, the differences did not reach statistical significance. This finding suggests that placebo use should be continued for newer agents being tested for all of the psychiatric disorders. These findings may help in the development of psychopharmacology trial designs and in the deliberations of ethics committees.