Why are placebos getting stronger?

But it turns out the placebo effect might not be as stable as we’ve assumed. Barsky recently published a study that looked at a bunch of antidepressant trials that had taken place between 1980 and 2005, and he found that in 2005 patients in these trials responded to placebos way more than patients did back in the 1980s.

“The placebo response was about twice as powerful than it was in the 1980s,” Barsky says. “That’s a pretty significant difference.”

In other words, placebos seemed to be twice as powerful as they were 30 years ago.

No one, including Barsky, really knows why the placebo effect appears to be changing. But Ted Captchuk, another Harvard professor who studies the placebo effect, says that placebo “drift” as it’s now known, appears to be real. He says it’s shown up in more than just antidepressant trials. And one possible explanation, according to Captchuk, is that there’s been a change in our expectations…

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.