The term “placebo” derives from the Latin phrase meaning “I shall please,” and entered pharmacologic use in the 1700s. Modern placebo responses represent a complex biological phenomenon that extends well beyond a simple psychological effect.

The total improvement observed in placebo groups reflects several factors, including natural disease fluctuation, spontaneous remission, regression to the mean, background therapy, reporting biases, the Hawthorne effect (or the change in human behavior or performance that happens simply because people know they are being watched or studied), and true placebo-related physiologic responses driven by treatment expectations and rituals.

Expectancy appears to be the strongest and most consistent driver of placebo response. Neurobiologic studies demonstrate activation of catecholamine, endogenous opioid, cholecystokinin and endocannabinoid pathways, with reproducible changes in brain networks involving the dorsolateral prefrontal cortex, nucleus accumbens, and rostral anterior cingulate cortex. These findings confirm that placebo responses are measurable biologic events rather than purely psychological phenomena.

Factors such as clinician empathy, perceived expertise and the therapeutic relationship further influence outcomes. Placebo effects are generally stronger with injections than oral therapies, and increase with greater clinical contact and more elaborate treatment rituals.

The opposite phenomenon, the nocebo effect, occurs when negative expectations lead to symptom worsening or increased adverse-event reporting. Both placebo and nocebo effects can substantially influence trial outcomes.

In rheumatoid arthritis, placebo ACR20 responses range from approximately 10% to 45%, with pooled estimates near 29% at 3 months. Meta-regression analyses of RA trials from 1999 to 2018 demonstrated rising placebo response rates over time, associated with shorter disease duration, lower baseline disease activity, evolving trial designs, and expectation bias.

Importantly, placebo responses affect objective measures such as C-reactive protein and erythrocyte sedimentation rate, indicating that biological and disease-related factors contribute significantly.

Placebo responses also vary across countries and rheumatic diseases. Lower-income regions tend to report higher placebo responses, while median placebo rates exceed 25% across many rheumatic disease trials, being lower in vasculitis.

Strategies to reduce placebo inflation include neutral patient communication, greater reliance on objective endpoints, assessment of expectancy and blinding integrity, active placebos, placebo run-in phases (and eliminating high placebo responders), re-randomization of placebo nonresponders, and three-arm trials incorporating untreated control groups. These approaches help distinguish true treatment effects from the many factors that contribute to placebo response.

Disclosures: McLain reports no relevant financial disclosures.

Add topic to email alerts

Added to email alerts

We were unable to process your request. Please try again later. If you continue to have this issue please contact customerservice@slackinc.com.