Since the 1930s, it has been known that patients’ symptoms can be alleviated using psychological and contextual means, as is the case with placebo effects. In a study published in Nature Human Behavior, researchers queried the extent to which placebo effects can be transmitted from providers to patients. By systematically testing for an interpersonal-expectancy effect in simulated clinical interactions, researchers sought to demonstrate the social transmission of placebo effects.

Three studies were conducted on 194 undergraduate participants assigned to play either “doctors” or “patients” in 48 simulated clinical interactions. The doctors were told they would be using “thermedol,” a cream with analgesic effects, and a control cream without those effects. In reality, both creams had no effects, but participants in the doctor role were told that thermedol was more effective for pain reduction. During the simulation, the doctors administered each cream and applied a thermal stimulation without revealing any difference between the 2 creams.

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In the first study, researchers measured whether the beliefs of participants in the doctor group affected the pain experience, skin conductance response (SCR), and pain behavior as indicated by facial expressions of participants in the patient group. The results showed that despite receiving equal levels of thermal stimulation, patients cited a belief that the thermedol was more effective than the control cream, reporting less pain with the thermedol treatment. Patients also reported lower SCR response and pain ratings from facial expression, based on models with thermedol treatment. Researchers also applied a pain expression model trained on doctor’s pain facial expressions to analyze doctors’ behaviors when interacting with their patients. While doctors were treating the patients with the thermedol, the doctors expressed less pain through facial expression. Additionally, patients reported perceiving the doctors as more empathetic as they delivered the thermedol treatment, implying that patients were sensitive to these changes.

The researchers performed 2 additional studies to confirm the results with a larger sample size and rule out possible habituation because of treatment order. Overall, the results of study 1 were confirmed in study 2; however, patients reported this only when the control treatment was administered before thermedol, with lower SCR only for the treatments in this order. Patients still found the doctors more empathetic with the thermedol treatment regardless of order. In the third study, with a design of control-thermedol-thermedol-control and participants completely blind to conditions, all results from studies 1 and 2 were successfully replicated. Study 3 additionally proved that the effects could not be the result of central or peripheral habituation.

Through this study, researchers were able to induce doctors’ beliefs about the thermedol treatment and showed that those beliefs were transmitted to “patients” through subtle shifts in facial expressions and possible changes in attentiveness between treatments. However, the researchers suggest that additional studies using actual physicians and patients are needed to understand the impact of these findings on clinical practice. Overall, these results highlight the importance of interpersonal-expectancy effects and their potential impact on treatment outcomes.

Reference

Chen PA, Cheong JH, Jolly E, Elhence H, Wager TD, Chang LJ. Socially transmitted placebo effects [published online October 21, 2019]. Nat Hum Behav. doi:10.1038/s41562-019-0749-5