"caution" until further, better-controlled trials are conducted. An updated 2021 systematic review and meta-analysis based on 11 studies also found a significant, albeit slightly smaller overall effect of open-label placebos, while noting that "research on OLPs is still in its infancy."

If the person dispensing the placebo shows their care towards the patient, is friendly and sympathetic, or has a high expectation of a treatment's success, then the placebo is more effectual.

Depression

In 2008, a meta-analysis

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