The placebo effect can still work, even if people know it's a placebo

"The placebo effect is real – even if you know the treatment you've been given has no medical value, research has concluded," the Mail Online reports. The study in question aimed to further understand how placebos – inactive or dummy treatments – work.

http://www.nhs.uk/news/2015/07July/Pages/The-placebo-effect-can-still-work-even-if-people-know-its-a-placebo.aspx