The second is that the symptoms of many illnesses naturally wax and wane. Coupled with this is a phenomenon known as regression towards the mean. This effect occurs because sufferers of disease tend to seek help, and even participate in scientific trials of new treatments, when their symptoms are at their worst. It so happens that a fair amount of information exists concerning these nonspecific effects. The authors reviewed a total of 204 scientific articles identified by a computerized search of the medical literature as well as 75 articles and 3 books uncovered by other means.
Surgical procedures generate placebo effects.
They also cause side effects such as drowsiness, headache, nervousness, insomnia, and nausea. Yellow capsules tend to be viewed as more stimulatory, while white pills tend to be seen as analgesics and narcotics. Injections may have greater effects than oral agents. Placebos can have adverse effects, including that of making symptoms worse. Even therapeutic agents have greater effects when patients expect benefits as compared to when they do not.