Placebos have improved outcomes in studies of chronic pain, anxiety, high blood pressure, angina, asthma, ulcers, Parkinson's disease and rheumatoid arthritis, said Irving Kirsch, a psychologist who studies placebos at the University of Hull in England.
Kirsch reviewed 35 clinical trials of antidepressants, submitted by drug companies to the FDA, and found that placebos did just as well as the real drug with moderately depressed patients.
The review, published last month in The Public Library of Science, also found only a small, "clinically insignificant difference" between placebos and the real drugs among patients who were severely depressed. Even so, Kirsch said that patients on antidepressants should talk to their doctors before stopping them.
So, how do placebos work their magic? Researchers have known for years that they trigger a biochemical response in the brain, releasing neurotransmitters such as dopamine that act as natural painkillers. They also know that packaging can enhance the effect.
If researchers wear white lab coats, talk in a soothing voice or somehow instill confidence in volunteers, the placebo is usually more effective, said Dr. Donald Price, a neuroscientist at the University of Florida who has studied the subject for 30 years.
Coloring a tablet red makes it work better than a white pill, he said. Showing volunteers the placebo as they receive it enhances its effect compared with telling a volunteer he will get it through an intravenous feed at some indeterminate future time, he said.
"Little things can make a big difference in terms of any benefit that accrues to the patient," Price said.
But Ariely's study is the first to show that a higher price might enhance a placebo's effect.
"This applies in a very broad way to human beings in a variety of settings," Price said. "It doesn't just apply to medicine. It's sort of a ubiquitous principle."
The pricing effect might also explain the reaction of 20 students at the California Institute of Technology who had their brains scanned while sipping wine they were told cost either $90 a bottle or $5 a bottle.
When they thought they were sipping the expensive stuff, the scans showed increased activation of the brain's pleasure center- even when they were actually sipping from the $5 vino.
"A lower price creates an expectation of inferiority," said Hilke Plassmann, the neuroeconomics researcher at Caltech who led the study. "The expectation is a crucial part of an outcome."
