On this topic, I have always been intrigued by Simone de Beauvoir's comments in the introduction to The Second Sex. She says: But we do not confuse the idea of private interest with that ofhappiness, although that is another common point of view. Are not womenof the harem more happy than women voters? Is not the housekeeperhappier than the working-woman? It is not too clear just what the word happy really means and still less what true values it may mask. There is nopossibility of measuring the happiness of others, and it is always easyto describe as happy the situation in which one wishes to place them. In particular those who are condemned to stagnation are oftenpronounced happy on the pretext that happiness consists in being atrest. This notion we reject, for our perspective is that ofexistentialist ethics. Every subject plays his part as suchspecifically through exploits or projects that serve as a mode oftranscendence; he achieves liberty only through a continual reachingout...

This isn't really an answer to your question but, rather, a point I find interesting about the framing of your question. (You could still ask your question in slightly different terms, of course...) Although the idea of a "placebo effect" is common, there is actually some reason to doubt that it is "well-documented". A recent article in the New England Journal of Medicine by Asbjorn Hrobjartsson and Peter C. Gotzsche, (May 24, 2001) argues tha t the trials aiming to establish a placebo effect are, for the most part, not sound. http://content.nejm.org/cgi/content/abstract/344/21/1594 For example, in some cases the studies don't take into account the fact that the condition of some percentage of people will improve without any medication at all. Although the studies compare people who take medication with people who take a placebo, they don't always compare people who take the placebo with those who take nothing. This, as you might expect, doesn't settle the question, but...