University of Michigan researchers say they are investigating the "placebo effect," in which pills with no medicinal value work in some people.
Placebos are used in studies to demonstrate whether a specific treatment is of value. Usually some patients in the research are given the medication being studied and others, a placebo.
But little is known about the types of people who tend to respond positively to placebos.
The University of Michigan Health System study involved people suffering from fibromyalgia -- a type of chronic pain typically involving tenderness, stiffness and fatigue.
"There is substantial evidence that the placebo effect has strong biological underpinnings, and that some individuals are more likely than others to demonstrate this effect," said Dr. Daniel Clauw, director of the U-M Chronic Pain and Fatigue Research Center.
"This study suggests individuals with greater hour-to-hour and day-to-day variability in their pain may be more likely to be placebo responders," said Clauw, senior author of the paper.
It is not clear if the findings are only present in fibromyalgia, or may also be seen in other chronic pain conditions, the researchers said.
The study appears in the journal Arthritis & Rheumatism.
Copyright 2005 by United Press International
Explore further: Billionaires' $10m gift to Yale stirs debate in China