Analyzing the results of 84 clinical trials conducted between 1990 and 2013 exploring drugs to treat neuropathic pain, researchers found that the placebo effect actually grew stronger over that time, but only in the U.S. In other words, placebo pills given in 2013 seemed to reduce American patients’ self-reported pain much more than they did in the 1990s.

A strengthening placebo effect has also been seen in trials for psychiatric drugs. And this has genuine consequences. Fewer pharmaceuticals are being approved because they can’t contend with the rising placebo effect.

So what is going on?