The placebo response is a wonderful demonstration of the potential of the mind to bring about almost magical healing powers. But though there has been an amazing surge of knowledge about the placebo response over the last several years, there is still much we don’t know, and I think the most exciting times are yet to come. Here are some of the questions I think are particularly interesting, mainly because their answers have important clinical implications.
Not everyone is a “placebo responder”. Why? Perhaps we’ve been looking at this question the wrong way. We’ve been asking, “what makes a placebo responder?” The answer to this question has proven elusive. Perhaps we should be asking, “what prevents someone from being a placebo responder?” We actually already have one answer to this latter question. A fascinating study by Benedetti et al (1995) has shown that Cholecystokinin(CCK) acts to limit placebo responses. When given a CCK antagonist (e.g., proglumide) a considerably larger placebo response occurs. So CCK limits the placebo response and a drug that removes CCK from the picture, removes this limit. For this reason, the CCK antagonist proglumide has been called a “placebo amplifier”.
The CCK discovery is a fascinating one but the question of what limits the placebo is far from fully answered. CCK cannot turn non-placebo responders into responders.
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