Placebos work best for pain, disorders of autonomic sensation, and disorders of factors under neurohumoral control

Shapiro defined a placebo as any treatment deliberately used for non-specific psychological or psychophysiological effect.1 That the placeo effect, a classic example of the mind-body relation, is as clinically undeveloped as it is pervasive may reflect the dominance of modern chemotherapy. The placebo depends on largely subconscious interactions between the doctor, the treatment process, and the patient1 2; it is the form of a treatment without its substance.

In practice, placebo treatment usually consists of a dummy medication or an intervention, which ranges from surgery to history taking. Placebo medication commonly operates through the administration of a substance, either pharmacologically active (a drug) or inert. The net effect of a given drug is thus the sum of the drug's pharmacological effects and the placebo effect associated with the act of treatment.3

The use of placebos raises important ethical questions3 4; if these can be answered can we exploit the placebo effect to benefit patients? We first need to consider the neurophysiology of the placebo effect. In the psychoneurophysiology of pain the model of cognitive versus somatic pain survives.5 In this paradigm somatic pain is linked to the source of nociception while the patient's awareness and cognition, probably …