For years, experts have known that placebos - fake injections and pills with no real medication - can improve the health of patients with pain, asthma, high blood pressure and angina.
Now they've learned that raising the price of a fake pill makes it work even better.
A report this week in The Journal of the American Medical Association shows that expectations - shaped by factors that include the price of a medication - play a key role in how we respond to pain relievers and our response to therapies for depression, cancer, stroke or heart attack.
The new report adds to a store of knowledge about placebos, a subject that has long fascinated scientists. Understanding placebos could unravel mysteries about the body's ability to heal itself, they say.
Experts do know one reason placebos work: They raise our expectations. Make someone believe that a tablet will make a headache disappear and it often does - even if it turns out to be a sugar pill.
"Expectations create a different reality for us, which we don't really appreciate," said Dan Ariely, a behavioral economist at Duke University.
Researchers typically use placebos as controls in clinical trials of medicines and other therapies. Some volunteers get the real drug, while others get identical-looking placebos. It's not unusual for placebos to work almost as well as, and in some cases better than, the drugs being tested.
In the latest study, Ariely applied electric shocks to the wrists of 80 volunteers before and after giving each one a placebo painkiller. He told half that the pills cost $2.50 each, and told the other half that they cost 10 cents apiece.
Bottom line: about 60 percent of the 10-cent group reported pain reduction from the placebo, compared with 85 percent of the "higher-priced" group. None of the test subjects, who received $30 for their trouble, actually received a painkiller.
"It says something about our expectations and how they shape reality," Ariely said. "Price is just one of the things we use to make inferences."
Experts say the results also show the importance of boosting the hopes of patients treated for a wide variety of ailments.
"Our response to any intervention is partly the result of the power of the intervention, and partly the result of our expectations going in," said Alan Bellack, a professor of psychiatry at the University of Maryland School of Medicine.
