The power of the placebo.

The placebo is much more than a control medicine in a clinical trial. The placebo response is the largest component of any allergy treatment and consists of two components: nonspecific effects (eg, natural recovery) and a "true placebo effect" that is the psychological therapeutic effect of the treatment. Belief in the beneficial nature of the treatment is a key component of the true placebo effect, and can be enhanced by factors such as interaction with the physician and the sensory impact of the treatment. Negative beliefs can generate a nocebo effect that may explain some psychogenic illnesses; this is the basis of much research in psychoneuroimmunology. An understanding of the placebo and nocebo effects is important for general allergy practice, and harnessing the power of the true placebo effect is a major challenge to modern medicine.