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Symptom Improvement Found Across Diagnoses With Placebo
Placebo treatment was found to improve symptoms across multiple disorders, though the level of improvement varied from diagnosis to diagnosis, according to a systematic review and meta-analysis published in JAMA Psychiatry.
“These findings may help in assessing the necessity and ethical justification of placebo controls, in evaluating treatment effects in uncontrolled studies, and in guiding patients in treatment decisions,” noted lead author Tom Bschor, MD, University Hospital, Technical University of Dresden, Germany, and co-authors. “These findings likely encompass the true placebo effect, natural disease course, and nonspecific effects.”
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Researchers sourced randomized clinical trials (RCTs) from MEDLINE and the Cochrane Database of Systematic Reviews, selecting the top 10 highest-quality and most recent placebo-controlled RCTs per diagnosis—90 total. Authors’ primary outcome was the pooled pre-post placebo effect sizes (dav), determined using random-effects meta-analyses.
In the total included 9985 placebo-treated participants, symptom severity was found to improve with placebo in all diagnoses. Pooled pre-post placebo effect sizes differed across diagnoses (Q = 88.5; df = 8; P < .001), with major depressive disorder (dav = 1.40; 95% CI, 1.24-1.56) and generalized anxiety disorder (dav = 1.23; 95% CI, 1.06-1.41) showing the largest dav. Panic disorder, attention-deficit/hyperactivity disorder (ADHD), post-traumatic stress disorder (PTSD), social phobia, and mania showed dav between 0.68 and 0.92, followed by obsessive-compulsive disorder (OCD) (dav = 0.65; 95% CI, 0.51-0.78) and schizophrenia (dav = 0.59; 95% CI, 0.41-0.76).
“Insights into the course of illness under placebo may aid in judging the urgency of specific treatments and help to understand the illness course in the absence of a specific intervention,” concluded Dr Bschor and coauthors. “A better understanding of placebo responses may improve treatments, especially in psychiatric disorders where confidence, conditioning, and belief play a significant role.”
