There was amazement all round when it was clinically proven that the effect of the most commonly used antidepressant was not significantly better than that of a placebo. But strangely enough, no one admires the effectiveness of the placebo. A placebo effect is any and all effects of a pill not caused by its specific chemical composition. For example, a red, yellow or orange pill is associated with a stimulating effect, while blue and green pills are thought to be calming.

A placebo can also have adverse effects. It can make a person nauseous or give them stomachache. People even get addicted to it, and develop withdrawal symptoms when the placebo treatment is terminated. There is thus sufficient reason to be interested in the effectiveness and the neurobiological mechanism of action of placebos.

Placebo effects are due to unconscious changes in brain functions, which ameliorate the disease symptoms. This is caused by the patient’s expectations of the treatment. The substances in a placebo are indeed pharmacologically inert, but the effect of the information about it given to the patient and the patient’s own expectations can make the placebo effect very specific. This is true not only for pills, it also applies to conversational therapies and surgical interventions.

Parkinson’s

In Parkinson’s disease, which is caused by a shortage of the chemical messenger dopamine, a placebo can stimulate the release of more dopamine in the brain and thus amelioration of the symptoms. Parkinsonian symptoms can also be lessened by electrically inhibiting a deep region of the brain through an electrode inserted into it. If the doctor tells the patient that he is turning the stimulator of this deep electrode on or off, but actually does nothing, an improvement or worsening of the Parkinsonian symptoms immediately becomes evident.

In a test of Parkinson patients who have a deep electrode inserted in their brain while conscious, an inactive substance claimed to be a new anti-Parkinson product was injected during the operation. The electrical activity in the same brain region was reduced and the symptoms improved in about half of the patients. Apparently, the brain of a patients who responds to the placebo “knows” in which area of the brain the activity must be altered to lessen the symptoms. And this works better if the patient expects the “new product” to have an effect.

Self-healing brain

Depressed patients treated with a placebo had improved after six weeks to the same level as the patients who were given real antidepressants. Brain scans showed that the changes in activity of various brain regions were very similar between the group that was given the placebo and the group that was given the real antidepressant. The brain induces exactly the right changes in function that will lead to a reduction in the symptoms of depression because of the placebo.

If a patient in pain is given a placebo, then the brain “knows” that an augmented release of morphine-like substances and a displacement of activity in several brain regions and the spinal cord are required to suppress the pain. In contrast, the patient’s expectation that a painkiller will help is absent in Alzheimer patients. Thus, pain relief in these patients is less effective, and they require higher doses of painkiller to achieve the same result.

The placebo effect shows the unconscious capacity of the brain to heal itself. That mechanism can contribute little or nothing to the treatment of cancer, but seems to be effective in several brain disorders. Research into the mechanism of placebo effects and the question of why some of us are more susceptible to placebo effects than others could have important clinical consequences. In addition, we must definitely not underestimate the effect of the old-fashioned, imposing and confidence-inspiring doctor as a “walking placebo”.

Dit verhaal is geplaatst op donderdag 19 maart 2009 om 08:47 uur.