A bitter pill

“When new drugs are put on the market, clinical trials determine whether they perform better than inactive pills known as ‘placebos’. Research shows that over the last 25 years the difference in effectiveness between real drugs and these fake ones has narrowed - but more in the US than elsewhere. Are Americans really more susceptible to placebo effects, or is something else going on?”

http://www.bbc.com/news/magazine-34572482

“In 1996, pain-relieving drugs were on average 27 percent more effective than the placebos. By 2013, the placebo response had risen so much that the drugs were only 9 percent more effective.”

https://ricochet.com/americans-and-placebos/

(I would say advertising and expectations. The increase of ads, especially TV advertising, has increased tremendously in the last 15-20 years, and Americans have become more ready to believe in the effectiveness of any pill or capsule. People expect a pill to work; therefore, it does.)