has been known placebo and nocebo effects placebo and nocebo effects placebo and nocebo effects placebo and nocebo effects placebo and nocebo effects placebo and nocebo effects placebo and nocebo effects placebo and nocebo effects placebo and nocebo effects placebo and nocebo effects placebo effect placebo and nocebo effects placebo and nocebo effects has been known placebo and nocebo effects 30 percent of people: placebo and nocebo effects placebo and nocebo effects placebo effect