[Mari]

This article says that the Placebo effect has increased since the 1980s.

http://www.npr.org/templates/story/s...ryId=124367058

But also, says Kaptchuk, it could be that because drug companies mostly pay for drug experiments, doctors who do the research have a subtle incentive to say the drugs are working. And since doctors don't know who's taking a real pill and who's not, the fact that they see benefits in all patients would also inflate the placebo effect.

Then there's another possible explanation.

Researchers, especially in pharmaceutical trials, get paid for every patient they recruit. But often, Kaptchuk says, it's hard to find people, so doctors will sometimes admit patients to trials who simply aren't that depressed. And typically, he says, people who aren't that depressed are much more susceptible to the placebo effect.

"I don't think there's out-and-out fraud," says Kaptchuk. "I think that you're under pressure to recruit. It's really hard to recruit people. And you know, (when) it's borderline, (you) put them in. And those people on the borderline at the end, they are better in the placebo group."

Whatever the cause, placebo drift is something that has the potential to cause real mischief in medical trials.

"If the placebo response — that baseline — is shifting all the time, then it really confuses the issue of whether the drug is effective or not," Barsky points out.