I would speculate that when placebos appear to work, it is primarily
because they don't do anything, besides possibly providing some
increased hope to the patient, allowing the body to work without the
"side" effects of drugs. The human body naturally tries to heal
itself to the best of its ability.
Here's a very interesting example of placebos being administered on a routine basis, for years.
Natural Hygiene, as it is today, can be traced back to Dr Isaac
Jennings (of Oberlin, Ohio, USA) who, after practising medicine for 20
years, began to ask questions when, during a fever outbreak in the
summer of 1815, a patient who rested, drank water and did nothing,
recovered in absolute record time compared to patients who had been
medicated. Based on this, Dr Jennings noted similar results with many
other patients.
He then went on to treat many patients with what must have been one
of the first placebo (dummy pill) treatments. In 1822 he gave up
medical pills, plasters, powders and potions and treated patients with
pills made from bread and vegetable-coloured water for the next 20
years. This he only did to keep the patients’ confidence in him. He
would then advise his patients to correct their lifestyle and diet to
a more natural approach. He then practised for a further 20 years the
"do nothing mode of treating disease." He wrote three books, "Medicine
Reform" (1847), "Philosophy of Human Life" (1852) and "Tree of Life"
(1867).
Natural hygiene was often referred to at this stage as Orthopathy
meaning TRUE or RIGHT AFFECTION or BEHAVIOUR.
Dr Jennings had a great influence upon Dr R T Trall, who went on to
do more for the hygiene movement than any man, next to Dr Herbert
Shelton.I've read this account on other sites as well. The Jennings story can be verified by other sources online. His deliberate use of placebo for so many years is fascinating.
More information here on Jennings: http://naturalhygienesociety.org/past2.html