Placebo effect can be a social thing

Researchers have found the placebo effect, where a medical treatment with no active ingredient still works, is “contagious” and can be passed on from doctors to patients.

The finding, reported in the journal Nature Human Behaviour, suggests doctors with a stronger belief in their treatments may enact a self-fulfilling prophecy, unwittingly delivering more effective medicine.

The placebo effect is well established. Simply believing an injection will take pain away can make it work, even when the syringe is just full of saltwater.

Those expectations drive powerful changes in the brain, releasing the body’s own internal pain killers or “endogenous opioids”, which then faithfully deliver up the result.

But the researchers, led by Luke Chang from Dartmouth College in New Hampshire, US, were intrigued by evidence that the beliefs of the “treater” can also influence whether something works.

For example, when school teachers are led to believe certain students are “growth spurters”, those kids do better on a standardised test at the end of the year.

What would happen, the authors wondered, if you could get doctors to think a medicine was stronger than it actually was. Would their patients do better on it?

Unfortunately, they couldn’t get their hands on any real doctors, so they had to settle for that tried and tested human lab rat – the psychology student.

They called on 194 students to act as either doctor or patient in an experiment where the patients were given painful, but not injurious, heat stimulation to the forearm.

Two gels were applied to their arms to see if that helped the pain. The patients didn’t know what was in the gels, but the doctors did. Or at least they thought they did.

The doctors believed one gel was just petroleum jelly and wouldn’t do anything. They also thought the other gel was “thermedol” and that it was a good painkiller.

Sadly, all those wanna be doctors had been duped.

Thermedol was just petroleum jelly too. The doctors believed it worked because when they got the heat treatment themselves earlier, it was applied to their forearms and seemed to help.

It hadn’t. The cunning researchers had just turned down the temperature on the heat stimulator.

The doctor stooges were fully primed, and the scene was set for the consultation.

The doctors now gave thermedol to their patients, who promptly reported that it was a better painkiller than the other gel. And it wasn’t just their say so – the thermedol patients also had less perspiration, a sign their nervous system registered less pain.

It was clearly a placebo response. But the patients were blind to which gel was thermedol, so where was the placebo response coming from?

The doctors, would you believe?

The researchers had strapped cameras to the patients’ heads that were recording the doctors’ facial expressions. They had also trained a sophisticated AI algorithm to recognise a look of pain on the doctors’ faces.

A less pained expression by the doctor, it turned out, correlated very neatly with the pain relief patients got after thermedol.

On the other hand, it seems doctors were unconsciously “wincing” as they gave the other gel, which they thought wouldn’t work.

“Doctors appeared to convey more information relating to facial displays of pain when administering the control treatment, which they believed was ineffective,” the authors write.

Doctors were, in effect, transferring their own placebo response to thermedol to their patients, something the authors call the “socially transmitted placebo effect”.

Which, if you think about it, could come in very handy in an actual medical clinic.

“This finding… highlights the importance of explicit training in bedside manner when delivering information and interventions,” the authors write.

“[R]esources invested in discovering new treatments should be complemented by additional investment in understanding the mechanisms underlying one of the oldest and most powerful medical treatments – healers themselves,” they conclude.