科学美国人60秒:Different Placebos Can Have Different Effects

When it comes to providing pain relief, expectations can be a powerful prescription. That’s part of the theory behind the placebo effect, in which people often report feeling better—even after a sugar pill or sham procedure—simply because they expect improvement.

Now a study finds that there may be levels of placebo effect.

Forty-five healthy volunteers had a heating electrode placed on their skin to cause discomfort. Over multiple sessions, they were either given nothing, or Tylenol, or needle-free acupuncture or electro-acupuncture, in which the needles carry a slight current.

Painkillers should let them tolerate the heat longer. The hitch was that the Tylenol and needle-free conventional acupuncture were fakes.

The subjects were later interviewed about their expectations. And their feelings about each treatment largely determined its effect. Those who thought the acupuncture would work were more likely to report pain reduction from both the real and fake acu-treatments. The findings are in the journal PLoS ONE. [Jian Kong et al., Are All Placebo Effects Equal? Placebo Pills, Sham Acupuncture, Cue Conditioning and Their Association]

They suggest a variable placebo effect, one that may depend on whether you swallow that sugar pill with a grain of salt.

—Katherine Harmon