Placebo is the most studied therapeutic agent in neuroscience as the sole intervention that has been studied in all psychiatric disorders. However, despite its extensive study history, placebo has not been directly compared as a therapeutic across psychiatric disorders. A recent systematic review and meta-analysis in JAMA Psychiatry sought to determine which psychiatric disorders exhibit the largest improvement with placebo treatment in randomized clinical trials (RCTs). The study used 90 high-quality RCTs encompassing nine different disorders: major depressive disorder, generalized anxiety disorder, panic disorder, attention-deficit/hyperactivity disorder, posttraumatic stress disorder, social phobia, mania, obsessive compulsive disorder, and schizophrenia.

Overall, the analysis consisted of 9985 participants, with cohort sizes varying between disorders (Figure). The study found significant improvement with placebo treatment for all nine disorders, but degree of improvement varied significantly. Patients with major depressive disorder experienced the greatest improvement, followed by those with generalized anxiety disorder, panic disorder, attention-deficit/hyperactivity disorder, posttraumatic stress disorder, social phobia, mania, and OCD. Patients with schizophrenia benefited the least. Improvements were generally more pronounced in studies that had a larger female cohort, suggesting that female psychiatric patients may benefit more from placebo treatment than males.

Overall, this study justifies the use of placebo in psychiatric research, especially in psychiatric disorders where confidence, conditioning, and belief play a significant role. It also highlights how understanding differential placebo responses across disorders can enhance our knowledge, aid in interpreting clinical trials, assist in treatment decisions, and improve treatment strategies.

Reference:

Bschor T et al. JAMA Psychiatry. Epub ahead of print. Abstract