REVIEW OF: Bschor T et al, JAMA Psychiatry 2024;81(8):757–768

STUDY TYPE: Systematic review and meta-analysis

Placebo responses are a well-known feature of psychiatric care, but until now, clinicians have lacked clear data on how those effects differ by diagnosis. This meta-analysis provides a comprehensive look at placebo responses across nine major psychiatric disorders, offering context care ­strategies.

The authors analyzed 90 high-quality RCTs across nine psychiatric diagnoses: major depressive disorder (MDD), generalized anxiety disorder (GAD), panic disorder, ADHD, PTSD, social phobia, mania, OCD, and schizophrenia. Only placebo groups were included. The primary outcome was pre-post symptom improvement, measured by effect size, or the magnitude of change during the trial. The analysis also examined whether gender composition, study duration, or placebo probability influenced the magnitude of response.

Results

Placebo responses were moderate to large across all diagnoses:

• Large effects: MDD (effect size: 1.40), GAD (1.23), panic disorder (0.92), ADHD (0.88), and PTSD (0.84)
• Moderate effects: Social phobia (0.72), mania (0.68), OCD (0.65), and schizophrenia (0.59)

Effect sizes in MDD and GAD were comparable to or greater than those seen with active medications in some studies. Trials with a higher proportion of female participants showed a 0.2-point increase in effect size for every 25% increase in female representation. Placebo effects in PTSD varied widely, ranging from negative to very large, likely due to patient-specific and contextual factors. Most included trials were short term (2–13 weeks), which may account for some of the effects, as placebo responses are known to diminish over time. 

CARLAT TAKE
Placebo effects can be substantial, and this analysis captures them when they’re likely to be largest. Clinically, a placebo response can be just as beneficial as a “real” response—the difference being that the former is likely to wane over time. So use early gains to build an alliance and encourage lifestyle changes that can mitigate any diminishing returns later.