EDITOR'S NOTE: Ten years and $2.5 billion in research have found no cures from alternative medicine. Yet these mostly unproven treatments are now mainstream and used by more than a third of all Americans. This is one in an occasional Associated Press series on their use and potential risks.

People looking for natural cures will be happy to know there is one. Two words explain how it works: "I believe."

It's the placebo effect — the ability of a dummy pill or a faked treatment to make people feel better, just because they expect that it will. It's the mind's ability to alter physical symptoms, such as pain, anxiety and fatigue.

In just the past few weeks, the placebo effect has demonstrated its healing powers. In tests of a new drug to relieve lupus symptoms, about a third of patients felt better when they got dummy pills instead of the drug.

The placebo effect looms large in alternative medicine, which has many therapies and herbal remedies based on beliefs versus science. Often the problems they seek to relieve, such as pain, are subjective.

"It has a pejorative implication — that it's not real, that it has no medicinal value," said Dr. Robert Ader, a psychologist at the University of Rochester in New York who has researched the phenomenon.

But placebos can have real and beneficial effects, he said.

"Much of the results of certain alternative procedures are largely placebo effects, unless you believe there are people who exert magical powers so they can hold their hands over your body and cure you of disease," Ader said. "Make you feel better? That's entirely possible, especially if you believe it."

The placebo effect accounts for about a third of the benefits of any treatment — even carefully tested medicines, scientists say. This dates to a landmark report in 1955 called The Powerful Placebo. Viewed as groundbreaking, the analysis of dozens of studies by H.K. Beecher found that 32 percent of patients responded to a placebo.

Later studies found that dummy pills could raise pulse rates, blood pressure and reaction speed when people were told they had taken a stimulant; the opposite occurred when people were told that a drug would make them drowsy.

How does it work? Scientists do not always know, but there are many possible ways. Brain imaging shows that beliefs ("I know these pills will help") can cause biological changes and affect levels of chemical messengers and stress hormones that signal pain or pleasure.