Harvard Mental Health Letter

In Brief: When expectation fails

In Brief

When expectation fails

Treating the physical symptoms of people with Alzheimer's disease is difficult because they cannot easily identify or explain their needs. An experiment reveals another problem. Any treatment is likely to be less effective for them, because they lose the benefit of the placebo response.

The study compared hidden and open administration of a painkilling drug to 28 patients with Alzheimer's disease and 16 healthy controls matched for age and sex. All had veins on the back of the hand punctured for blood samples on two consecutive days. This often causes a burning sensation that is treated with lidocaine, a local anesthetic.

On one day, the lidocaine was administered in full view and patients were told that the pain would go away quickly. On the other day, they were not told that they were being given lidocaine. All rated their pain on a scale from 1 to 10 before and after the needle prick. Heart rates were also recorded as a measure of anxiety. The purpose was to distinguish the placebo response — the result of expecting relief — from the specific effect of the local anesthetic.

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