The placebo effect involves showing a response to non-active formulas in clinical trials. Non-active formulas are used as a control condition to establish whether the active formulas are more effective for symptoms than what would normally be observed simply due to expectations that the medications are effective. The medication being tested should result in greater improvements in symptoms than placebo if their active ingredients are doing what they are meant to do. The placebo response can include both improvements in symptoms as well as adverse reactions that have been associated with the medication being tested.

What is the evidence for placebo response?

Moderate quality evidence suggests greater response to active medications than to placebo for both mania and depression symptoms. This was found in both adults and children with bipolar disorder. Response rates to active medications was around 49% for mania and 52% for depression. Response rates to placebo was around 32% for mania and 39% for depression. Greater response to active medications for mania, but not for depression, was related to greater relative efficacy (comparing active medications to placebo). Greater response to placebo for mania, but not for depression, was related to decreased relative efficacy.

Moderate to low quality evidence suggests longer treatment duration increased the likelihood of placebo response for depression. Greater depression symptom severity at baseline (start of treatment) increased the likelihood of response to active treatment for depression. People with mania and psychotic symptoms, and people who completed the trials, were more likely to have active drug-associated improvements in mania symptoms. People with mixed-state diagnoses were less likely to have active drug-associated improvements in mania symptoms. Increased placebo response for mania was associated with older patients’ age, and female sex. Studies conducted in the USA or Europe (vs. other regions), and studies conducted over three or more regions (vs. fewer regions) were more likely to report greater placebo response.

November 2021

Image: ©Dariusz T. Oczkowicz, ars digital media services – stock.adobe.com

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