Asthma symptom changes reflect placebo effect

Placebo treatments can improve patients' self-reported asthma symptoms but not their lung function, say U.S. scientists.

The study, carried out by Harvard Medical School researchers and published Thursday in the New England Journal of Medicine, concludes that patient assessments are unreliable since they report improvement when there is none.

Thirty-nine patients with chronic asthma completed the study that compared four interventions: an inhaler containing a bronchodilator; two placebos — either a placebo inhaler or sham acupuncture; and no intervention.

Placebos are treatments that have no active ingredients or physiological effect. They are used to test the effectiveness of a 'real' therapy. However, numerous studies have reported on the 'placebo effect,' where the sham treatment has a benefit for a patient.

The researchers randomly administered one of the interventions to each study participant, during sequential medical visits that were three to seven days apart. Participants were unaware what treatment they were receiving, although most believed they were receiving active treatment.

The procedures were repeated in two more blocks of visits, such that each patient had a total of 12 medical visits. At each visit,