Commonly, patients who respond to an antidepressant ask whether they’re merely experiencing a placebo effect. What they may not know is that the placebo has fallen on hard times. Progressively, steadily, depression researchers have seen a weakening in the case for classic placebo effects, the argument that when antidepressants work, the engine is hopeful expectation.
The latest damage comes from a reassessment of trends in drug research. 14 years ago, researchers at Columbia made note of a disturbing pattern. In antidepressant trials, placebo response rates had been rising steadily, year by year, decade by decade. Where, in 1980, perhaps 20 percent of participants on dummy pills showed substantial improvement, by 2000, the rate was 30 percent. Later, response rates of 35 or 40 percent became common.
"What has disappeared from the equation is the classic placebo effect. The notion that depression is highly placebo responsive, and more particularly the notion that antidepressant effects are basically placebo effects, has become ever less plausible and ever harder to defend."
What was causing the change? For observers who put stock in classic placebo effects, the answer was simple. As antidepressants gained acceptance—as more people came to believe that they work—the mere fact of taking pills stimulated improvement arising from faith in their powers.
But what if placebo response rates have not been on the rise after all? We might conclude that increased acceptance of antidepressants does not result in greater efficacy for dummy pills. We would want to say that the classic placebo response, the one grounded in hopeful expectations, is not powerful after all.
Sure enough, an international team of researchers has just provided a new, more detailed and comprehensive analysis of antidepressant studies. It finds that, at core, placebo response rates have been stable for 25 years and more.
Yes, in the raw data, dummy pill effects look to have been on the rise—but that’s because of changes in the way the trials have been conducted. Comparing like to like—looking at similar studies—the impact of dummy pills has not budged.
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