The placebo effect could be driven by mechanisms unrelated to whether or not you believe you’re being treated and still mean pretty much the same thing—similar to priming, it could just be that mentioning the right words before giving people a sugar pill is enough, you don’t have to actually make them believe you’re giving them a painkiller.
To repost skeptical lurker’s link: http://www.guardian.co.uk/science/2010/dec/22/placebo-effect-patients-sham-drug
The placebo effect could be driven by mechanisms unrelated to whether or not you believe you’re being treated and still mean pretty much the same thing—similar to priming, it could just be that mentioning the right words before giving people a sugar pill is enough, you don’t have to actually make them believe you’re giving them a painkiller.