Why do placebos work?
The placebo effect is a fascinating phenomenon, possibly one of the most fascinating in medicine.
For some reason an individual will respond to an inactive agent in a positive manner. The word comes from the Latin 'placere, meaning 'to please.' It is generally thought that the effect is entirely in the mind of the patient.
Recent research from Germany, however, suggests that this may not be the entire case. Using modern imaging technology the researchers found that simply believing a pain treatment is effective actually dampens pain signaling in a region of the spinal cord called the dorsal horn, suggesting that a powerful biological mechanism is at work.
Placebos are used in scientific trials, usually double-blind trials, in which neither the patient nor the doctor knows whether they are being given an active agent or a placebo. This sort of trial is used to assess whether an active agent or drug is superior to the placebo, ie, better than nothing.
The problem is that a placebo response can occur in anything between 25 and 70 per cent of cases. The frequently reported placebo response is 30 per cent, but it depends upon many factors. In general, the more dramatic the treatment, the greater the placebo response.
In studies on medicines, it has been found that red, yellow or brown tablets or capsules work best, whereas green and blue work less well. It has also been found that the smaller the tablets or pills the better, on the principle of multum in parvo (Latin for 'much in little').
Before the Second World War, placebos were prescribed liberally. The Latin names may have helped boost their efficacy. For example, tinctura cardamomi compositae (a mixture of cayenne pepper, caraway, cochineal, glyerin and alcohol), worked well as a tonic and was extremely popular. Nowadays placebos are not prescribed in clinical settings, other than in research trials.
In the study from Germany the researchers applied painful heat to men's arms and compared their spinal cord responses when they thought they had been treated with either an anesthetic cream or a placebo. In actual fact, both creams were placebos, but the scans showed nerve activity was reduced significantly when subjects believed they were getting the anesthetic.
This has huge potential importance. The researchers believe that the placebo causes the body to release endorphins and other neurotransmitters that produce a biological effect. This is totally different to the standard theory about placebos, which suggests that the individual merely 'thinks' his or her symptoms are less. It could open up a new field of research with huge potential for new types of pain
treatment.
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Wednesday 23 May 2012
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