A doctor or nurse's facial expression could be the difference in whether a painkiller works or not, a new study has found.
Scientists in the US have found if a healthcare provider is convinced it'll work, there's more chance it actually will, regardless of whether it actually works or not - and patients pick up on that through thier facial expressions.
Researchers at Dartmouth College in New Hampshire took nearly 200 college students and divided them into two categories - doctor and patients. The doctors were given two creams, and told one was a painkiller called 'thermedol', and the other a placebo. The patients - unaware which was which - were administered heat-based pain stimulation, and asked to rate the effectiveness of the two creams at reducing pain.
Patients reported thermedol was better, and looked visibly in less pain - but there was a catch.
"In actuality, both creams were identical petroleum jelly-based creams with no analgesic effects," the study, published in Nature Human Behaviour on Tuesday, revealed.
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In other words, the only difference between the two creams is that the doctors thought one of them would work, and the other one wouldn't.
But how? While it's been known for decades that placebo treatments can work even if the patient knows it's a placebo, in this case they had no idea - only the doctors had that knowledge.
"We speculate that there are at least two possible mechanisms underlying the socially transmitted placebo effect," the scientists write. "One possibility is that the doctors send some nonverbal information that communicates their beliefs about which treatment is more likely to be the active treatment.
"Alternatively, the doctor might be more attentive to the patient and develop a more empathetic connection which ultimately makes the patient feel better when they are receiving pain stimulations. The patient may then incorrectly attribute this analgesic effect to the thermedol treatment."
While the study was carried out with students, the authors say the effect should be even stronger in the real world.
"The fact that even participants with no medical expertise or training showed transmitted placebo effects through a brief social interaction in a highly controlled laboratory environment indicates that the influence of doctors' expectations on patients' outcomes will probably be even larger."
They say in addition to the investment in new treatments, the study shows there should be more money spent "understanding the mechanisms underlying one of the oldest and most powerful medical treatments - healers themselves".
"This finding has important implications for virtually all clinical interactions between patients and providers and highlights the importance of explicit training in bedside manner when delivering information and interventions."