Subjective experiences of pain can be influenced by a healthcare providers’ expectations of treatment success, according to research published in the journal Nature Human Behaviour. The findings indicate that placebo effects can be socially transmitted during interactions between doctors and patients. The study also suggests there is a causal link between providers’ expectations and patients’ treatment outcomes.

“I originally trained as a clinical psychologist and have had a longstanding interest in how therapy works — why do patients actually get better? There has been growing interest in the role of mechanisms of psychotherapy that are common across therapies, often referred to as common factors, in contrast to focusing on the specific factors of a particular brand of therapy,” said study author Luke J. Chang, an assistant professor and director of the Computational Social Affective Neuroscience Laboratory (Cosan Lab) at Dartmouth College.

“Common factors include things like expectations and the therapeutic alliance between the doctor and patient, but have been difficult to systematically study. While it has been known for many years that doctors’ expectations likely influence patient outcomes, the magnitude of this effect has never really been investigated.

Double-blind trials, in which neither participants nor experimenters know who is receiving a particular treatment, have become the gold standard for research.

But “for some types of trials (e.g., psychotherapy), treatments can never be double-blind as the provider needs to know which treatment they are delivering,” Chang explained to PsyPost. “It has been estimated that aspects of the clinical relationship such as perceived empathy, trust, connection, and expectations can influence clinical outcomes, but most medical treatments have focused on the biological bases of treatments and have largely downplayed the influence of the provider.”

In three experiments, 194 participants were randomly assigned to play the role of either a doctor or a patient. The doctors were informed that they would be administering either a cream called thermedol or an inert cream. The creams were two different colors, but both were actually just a placebo — the petroleum-based jelly, Vaseline.

The doctors were told about the properties of the two creams and led to believe that thermedol alleviated thermal pain by targeting skin pain receptors. After each topical cream was applied to a patient’s arm, they received thermal heat (47 degrees Celsius/116.6 degrees Fahrenheit) and assessed the effectiveness of the cream.

The researchers found that patients who received the thermedol cream perceived less pain as a result of the treatment despite there being no real difference between the two creams. Recordings of the patients’ facial expressions also indicated that they experienced less pain when receiving the thermedol treatment.

“When the doctor thought that the treatment was going to work, the patient reported feeling that the doctor was more empathetic. The doctor may have come across as warmer or more attentive. Yet, we don’t know exactly what the doctor was doing differently to convey these beliefs that a treatment works. That’s the next thing that we’re going to explore,” Chang explained in a news release.

The findings indicate that “provider’s beliefs about treatment efficacy and how they interact with patients can impact patient outcomes beyond the specific treatment. I think this has implications for almost all types of healthcare providers,” Chang told PsyPost.

“We know a lot about the neurobiological mechanisms of placebo effects, but less about how these effects might be cultivated in real clinical practice. This study provides at least one example of how contextual cues and healthcare provider’s behavior can impact patients to create a placebo effect,” he added.

The study, “Socially transmitted placebo effects“, was authored by Pin-Hao A. Chen, Jin Hyun Cheong , Eshin Jolly, Hirsh Elhence, Tor D. Wager and Luke J. Chang.