Time has an interesting article on the Nocebo effect, The Flip Side of Placebos: The Nocebo Effect by John Cloud

Exactly why the placebo and nocebo responses arise is a puzzle, but a fascinating article in Wired magazine noted earlier this year that the positive placebo response to drugs has increased during clinical trials over the past few years. The article speculated that drug advertising — which exploded after 1997, when the Food and Drug Administration began allowing direct-to-consumer ads — has led us to expect more from drugs. Those expectations, in turn, have made us feel better just for popping a pill. (Placebo responses can also occur simply when you book appointments with doctors or psychotherapists.)

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Source: Time