Previous reviews have suggested that placebo benefits are restricted to subjective responses, like pain, the authors explain, but are ineffective for objective physiological outcomes.
Dr. Margaret E. Kemeny from the University of California, San Francisco, California and colleagues investigated whether there is a placebo response in objective measures of lung function in 55 patients with asthma.
The results of methacholine challenge tests improved significantly after administration of placebo, the authors report, although the response to salmeterol was significantly greater than that of placebo.
Placebo responders were significantly younger than nonresponders, the results indicate, but otherwise the groups did not differ on demographic and psychological characteristics.
The response to methacholine did not differ according to whether the physician emphasized positive expectations ("enhanced" encounters) or minimized such factors without introducing negative expectations ("efficient" encounters), the researchers note. This experimental manipulation of physician behavior "altered perceptions of the physicians but not the magnitude or frequency of the placebo response."
Dr. Kemeny and colleagues conclude: "The placebo response in patients with asthma is important in understanding the limitations of clinical research studies and in maximizing safe and effective therapies. This article confirms the existence of a strong placebo response in an objective and clinically relevant measure of disease activity."
J Allergy Clin Immunol 2007;119:1375-1381.
