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Experimental Studies of the Placebo Response

C. J. Lucas, M.B., M.R.C.P., D.P.M.

Medical Research Council, Clinical Psychiatry Research Group, Graylingwell Hospital, Chichester

ABSTRACT

Four experiments are reported in which the effect of a placebo in healthy subjects has been studied. The placebo was a small white lactose tablet which was administered orally and introduced as a drug with potential effects. For thirty minutes following the administration of the placebo the subjects recorded symptoms on a check list of 26 items, half of which were pleasant and half unpleasant.

In two of the experiments the subjects spent the thirty-minute observation period sitting alone (individual conditions) and in the other two, subjects were seated in groups of three (group conditions).

Before each experiment all the subjects completed the M.P.I.

Sixty-six per cent. of the subjects (N=59) reported one or more effects. Analysis of the data led to the following conclusions:

1. The total number of responses reported remained constant despite altering the conditions of administration (i.e. "individual" and "group").
   
2. The proportion of pleasant to unpleasant responses remained approximately one-half throughout the experiments.
   
3. The relationship between placebo responding and personality varied according to the conditions of administration. This was clearest for neuroticism where the correlation was high (r=·74) under "group" but insignificant under "individual" conditions.
   The interpretation of the correlations with extraversion was less clear. When homogeneous samples were tested the pattern of correlations was the converse for that of neuroticism, i.e. significant correlation under "individual" but insignificant under "group" conditions. However, when theological students, as opposed to nurses, were tested, the correlation became negative. A possible explanation was discussed.
   
4. "Stress" administration in which the importance of the research and the necessity for accurate observations were emphasized, increased responses.
   The findings, and their relation to those previously reported, were discussed in detail.