Fertility, depression, Parkinson’s, fitness, hunger levels, pain, and asthma are a few of the things the inert wonder drug can help treat.

Why did the placebo work—even after patients were told they weren’t getting real medicine? Expectations play a role, Dr. Kaptchuk says. Even more likely is that patients were conditioned to a positive environment, and the innovative approach and daily ritual of taking the pill created an openness to change, he says.

Do placebos work on the actual condition, or on patients’ perception of their symptoms? In a study published last year in the New England Journal of Medicine, Dr. Kaptchuk’s team rotated 46 asthma patients through each of four types of treatment: no treatment at all, an albuterol inhaler, a placebo inhaler and sham acupuncture. As each participant got each treatment, researchers induced an asthma attack and measured the participant’s lung function and perception of symptoms. The albuterol improved measured lung function compared with placebo. But the patients reported feeling just as good whether getting placebo or the active treatment.

“Right now, I think evidence is that placebo changes not the underlying biology of an illness, but the way a person experiences or reacts to an illness,” Dr. Kaptchuk says.

The list of evidence in the article at WSJ is impressive. I’m amazed by how our experience of medicine is so closely tied to the qualitative outcome of medicine.