"Definition: A placebo, as used in research, is an inactive substance or procedure used as a control in an experiment. The placebo effect is the measurable, observable, or felt improvement in health not attributable to an actual treatment.
When a treatment is based on a known inactive substance like a sugar pill, distilled water, or saline solution rather than having real medical value, a patient may still improve merely because their expectation to do so is so strong. "
-http://arthritis.about.com/od/arthritistreatments/g/placebo.htm
'Here’s an interesting take on this effect as it relates to sports supplements:
I’m sure some people are reading this and thinking, "But I know these products work because I’ve taken them and feel their effects!" While these perceived effects are potent, I submit to you that based on the scientific evidence, this is merely a result of the placebo effect.
The placebo effect is when someone uses an inert substance, which should produce no effect, yet somehow still experiences an effect. This occurs frequently when pharmaceutical companies test a new drug. They give one group the real drug and another group an inert sugar pill. Interestingly, the group receiving the sugar pill often has a series of side effects like dry mouth, headaches, dizziness, adding ten pounds to their bench, etc. — all caused by their own minds!
One famous research analysis calculated the placebo effect to account for 75% of a drug’s effect, although this exact figure remains controversial (19). '
'So how does all of this relate to the placebo effect? Well, if healing and cellular repair is accomplished most effectively during periods of RnR, then invoking that state will promote healing, well being, and long life. One of the things that does invoke feelings of rest and relaxation is love. It is well known that married people live longer lives (and it isn't just that it seems longer). The well known maternal "kiss it and make it better" treatment does relieve pain and presumably resets the RnR state. Presumably regular episodes of love and affection from a romantic partner can reset the RnR state too.
At the heart of energy metabolism is nitric oxide. A major determinant of whether an organism is in the FoF state, or the RnR state is the level of NO. Because NO is freely diffusible, and is created and destroyed at many sites in the body, the basal level has an impact on the signaling effects of NO. Low basal NO will affect every NO mediated signal with no threshold. This is an extremely important point. Anything that increases basal NO will shift physiology to the RnR state and away from the FoF state. There are many things that will do this, placebos are one of them. The relaxation response causes the production of NO. My own favorite method is via commensal ammonia oxidizing bacteria on the skin. No matter what the basal NO level is, physiology can always destroy that NO very rapidly with superoxide. Mitochondria have an essentially unlimited capacity to make superoxide, limited only by the supply of O2 and reducing equivalents. What ever the NO level is, mitochondria can pull it down to zero. This has important implications in acute respiratory distress syndrome, and is what is responsible for the multiple organ failure which sometimes occurs.
Long term meditation does result in reduced age-associated loss of cortical white matter. I presume by increased repair, improved energy status, reduced apoptosis, better clearing of damaged proteins, and perhaps increased axonogenesis. Many neurotrophic factors have effects mediated through NO.
Meditation modulates the immune system and increases antibody titers due to vaccination. Meditation reduces the symptoms of the metabolic syndrome and improves a number of heart health parameters.
If placebos increase NO levels and invoke the RnR state, then nocebos likely reduce NO levels and induce the FoF state. What conditions might be improved by the FoF state? In the earlier example, nausea was reduced by a nocebo. Much of the enteric nervous system is nitrergic that is the nerves generate NO. If the basal level of NO is reduced by a nocebo, then the response of the enteric nervous system to CNS generated nausea signals mediated by NO will be reduced by a nocebo and enhanced by a placebo. When running from a bear, it is a "feature" to delay vomiting.'
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http://daedalus2u.blogspot.com/2007/04/placebo-and-nocebo-effects.html
