A three-week trial of 90 healthy adults aged 65 to 90 found that those given a placebo pill, whether told it was fake or led to believe it contained active ingredients, showed changes on objective tests of short-term memory and physical performance that did not appear in a no-treatment control group, according to a study published in the International Journal of Clinical and Health Psychology. The trial, led by Diletta Barbiani and colleagues at the Universita Cattolica del Sacro Cuore in Milan, is described by its authors as the first to examine whether a placebo can affect functions that decline with age, rather than symptoms people report feeling, such as pain.
Participants were randomly split into three groups: one told the pills were an active multivitamin supplement (a deceptive placebo), one told plainly that the pills were inert but could still trigger a beneficial mind-body response (an open-label placebo), and one that received no pills at all. After three weeks, the open-label group reported lower perceived stress than both other groups and showed significantly better short-term memory performance than the no-treatment control group. Both placebo groups, open and deceptive, showed within-group improvements on a physical performance battery that did not occur in the control group, with the researchers noting the open-label group's gains were often as large or larger than the deceptive group's.
The researchers say the pattern challenges an assumption in placebo research that only deceptive placebos, not openly labeled ones, can move objective measures rather than self-reports. They also flagged a limit to the effect: measures of more stable traits, such as optimism and self-efficacy, did not change in any group, suggesting placebo effects in this trial were confined to shorter-term, situational states like stress and momentary task performance rather than fixed personality traits.