Chronic fatigue syndrome is a complicated illness. It has no known cause or cure. Symptoms include severe depression, muscle and joint pains, sleep and mood disturbances, and headaches.

A new analysis of the available information on the subject shows patients who are given placebo, or inactive, treatments respond at a much lower rate than doctors predicted. Only 19.6 percent of patients with chronic fatigue syndrome felt better after getting a placebo treatment.

The researchers had expected the rate to be as high as 50 percent because diseases with highly subjective symptoms tend to respond well to placebo treatments.

The review was reported in a recent issue of Psychosomatic Medicine. The researchers studied data from 29 studies involving more than 1,000 chronic fatigue patients who were given placebo treatments.

As a possible reason for why placebos do not usually work, the authors of the study say patients may not really expect any treatment to work. Also, the differences between how doctors and patients view the illness could "impede development of a collaborative therapeutic relationship," reviewers suggest.

Doctors who work with chronic fatigue patients say a greater sympathy from doctors for patients may help create more effective treatment options.