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Your beliefs affect the strength of the placebo effect

How do your beliefs influence placebo effects?


Placebos are inert substances.

The placebo effect refers to any situation where body and mind are affected by an intervention to a greater degree than would be expected based on the intervention itself. Most commonly, we think of placebos as pills or shots that have no active medical ingredients in them that lead to improvement in health. Placebo effects are incredibly powerful.

A fascinating paper by Baba Shiv, Ziv Carmon, and Dan Ariely in the November, 2005 issue of the Journal of Consumer Research explored how placebo effects are influenced by what people know about the placebo.

In a series of studies, these researchers had people imbibe an energy drink that was advertised as affecting people's mental ability. To determine the effect of the drink on people's performance, they measured the number of words that people were able to unscramble. The key aspect of the study focused on the information that people were given about the drink.


The brand SoBe was used as the placebo in these studies.

In one study, people were told about the effectiveness of the brand SoBe, which is a real product. One group was told that a large number of studies suggest that drinks like this create large improvements in mental functioning. A second group was told that the drinks provide a slight improvement in thinking. Participants were also told about the cost of the drink. Half of the participants were told that the drink cost its regular price ($1.89), while a second group was told that it was purchased at a discount ($0.89). Finally, a control group performed the word-unscrambling test without hearing about the drink at all.

The control group unscrambled 7 words correctly. Those people who read that the drink was not so effective generally did worse than the control group, while those who read that the drink is highly effective did better than the control. The price of the drink also affected performance. Those who got the discounted drink also performed worse overall than those who received the full-price drink. Indeed, the people who got the worst combination of information (the drink is only slightly effective and was low-priced) unscrambled only about 4 words correctly, while those who got the best combination of information (the drink is highly effective and regularly priced) identified over 10 words correctly.

As part of the study, people were asked to rate how effective they thought the drink would be at influencing their thinking ability. These ratings were a good predictor of people's performance. That is, the more that people believed in the drink, the more that it had an effect on the number of words they unscrambled.

These results are quite important for thinking about placebo effects. You might think that you get placebo effects just from being a part of an intervention. For example, you may learn that taking a pill makes you feel better, and so your body may react in ways that make you feel better whenever you take a pill.

These results suggest that part of the effect of a placebo is based on how much you believe in it. All of the factors that determine whether you think something will work as promised can influence placebo effects. That is why price affects the placebo effect. We normally think of discount products as being less effective than full-price products. That same belief also influences the placebo effect.

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