The placebo effect is often considered to be a psychological rather than a physiological phenomenon – patients only think they are better. But it is far more than that, as clinical trials have testified. In a Swedish trial of heart patients, for example, those in the placebo control group were given an identical pacemaker to those in the treatment group, but unbeknown to them, the device was switched off. After three months, astonishingly, the symptoms of patients in both groups had improved. More astonishing still, the researchers were able to measure the improvement in the patients in the placebo control group as an increase in the flow of blood from the heart (Linde et al., 1999).
http://www.scienceinschool.org/2011/issue21/placeboSSRI类西药是安畏型？