The first time placebos gained traction in medical literature was in the 17th century. Like many practices from that period, it seemed likely that the placebo effect would also be disproven by modern science. Not only is this not the case, but the placebo effect is still prominent to this day.

Now, researchers have shown that the effect can work even if people know they’re taking a placebo.

It’s surprisingly common for general practitioners to prescribe placebos. Most often, this a so-called impure placebo (a substance or treatment that has clinical value, but not for the condition for which it is being prescribed), rather than a pure placebo (a straight-up fake treatment, like a sugar pill). In the UK, 97% of general practitioners admitted to giving an impure placebo at some point during their career, and in the US and Germany, physicians also “routinely” give placebos.

It’s not clear just how often doctors prescribe placebos, but they seem to be prevalent in non-specific theories. These prescribed placebos can be surprisingly effective, but the key to the effect is the patient not knowing that it’s a placebo.

Or so we thought.

In a new study, researchers found that even nondeceptive placebos (where patients knew they were taking a placebo) can work. The implications for this are profound, researchers note.

“Just think: What if someone took a side-effect free sugar pill twice a day after going through a short convincing video on the power of placebos and experienced reduced stress as a result?” said Darwin Guevarra, MSU postdoctoral fellow and the study’s lead author. “These results raise that possibility.”

In the study, Guevarra and colleagues tested the effect of nondeceptive placebos on reducing emotional brain activity. They split participants into two groups, both of which received a placebo, but one knew it was a placebo, while the other didn’t.

The placebo group was first given material to read about the placebo effect and then asked to inhale a saline solution nasal spray — a pure placebo. The group was told that the spray was a placebo and contained no active ingredients, but it can help reduce their negative feelings if they believe it does. The control group inhaled the same saline spray but were told that the spray improved the clarity of the physiological readings the researchers were carrying out.

The researchers then compared the results in two experiments, one in which participants self-reported negative emotions, and one in which they measured biomarkers of emotional distress.

Within seconds, the effects of the nondeceptive placebos were visible.

“These findings provide initial support that nondeceptive placebos are not merely a product of response bias—telling the experimenter what they want to hear—but represent genuine psychobiological effects,” said Ethan Kross, co-author of the study and a professor of psychology and management at the University of Michigan.

This isn’t the first study to come up with this type of finding. In 2014, a different research group tested how participants react to migraine medication; one group was given a migraine drug labeled with the drug’s name, another took a placebo labeled “placebo,” and a third group took nothing. The placebo group exhibited around 50% efficiency compared to the drug group. At the time, researchers explain it by the ritual of taking medicine as a positive effect — even if people know it’s not medicine, the action alone stimulates the brain into thinking it is healed, and it works.

So what does this mean? Well for starters, it gives us a bit more insight into how placebos work, and on a more practical level, it could offer a valuable avenue for placebo treatment.

The medical action of prescribing a placebo is often shrouded in ethics concerns, and many doctors consider it unethical to prescribe placebos without the patient knowing. This could offer an alternative — if the patients know what they’re geting, the ethics conundrum is solved.

“Placebos are all about ‘mind over matter,” said Jason Moser, co-author of the study and professor of psychology at MSU. “Nondeceptive placebos were born so that you could possibly use them in routine practice. So rather than prescribing a host of medications to help a patient, you could give them a placebo, tell them it can help them and chances are—if they believe it can, then it will.”

Journal Reference: Darwin A. Guevarra et al, Placebos without deception reduce self-report and neural measures of emotional distress, Nature Communications (2020). DOI: 10.1038/s41467-020-17654-y