Why are placebos thought to be getting stronger?

I read the blog Wired from time to time to make some slight attempt to keep up with really cool innovations and products in the land of the wired.In doing so I came across an excellent essay on placebos. See here .

Here is one sample from the article:

"Two comprehensive analyses of antidepressant trials have uncovered a dramatic increase in placebo response since the 1980s. One estimated that the so-called effect size (a measure of statistical significance) in placebo groups had nearly doubled over that time." [Unfortunately, no references are given in the article].

If the placebo effect is getting stronger, why would that be?

One thought is that the direct to consumer drug company advertising has had effect(s) greater than simply promoting sales for a given medication.Perhaps it could generate greater belief in the effectiveness of pills in general which has stirred up a greater expectation of something good happening to people who take medications.Drug company advertising is just one force pointing in that direction;so do the activities of various disease promotion organizations (some of which are thought by some cynics to really be put-up jobs by the drug companies) and the general trend that seems to make almost everything a medical problem.

The "expectation effect" is a topic of relevance to the placebo effect. A patient can expect the announced beneficial effect of a pill and this has been shown in some experimental settings to increase the release of endogenous opioids. This article from Scientific American gives some detail and background regarding this issue.Areas of the brain that deal with weighting of events and threats seem to be activated by placebo through this mechanism of anticipation. Some studies have indicated that subjects who sign up a drug study may experience beneficial effect even while they are put on the waiting list.

Harriet Hall offers a detailed discussion of various issues related to the placebo effect here in the May 20th 2009 issue of the blog "Skeptic".

She outlines 4 possible ways placebo might work;

1.Expectation
2.Motivation (folks want to get better and often sign up for clinical trials)
3.Conditioning ( maybe all of us have become somewhat conditioned to believing pills make us better is in no small measure due to the effect of drug company and disease promotion groups advertising )
4.release of feel good substances such as endogenous opioids.