The effectiveness of a placebo is highly correlated to the expectation. If the expectation is positive it can heal, if the expectation is negative it will not heal and can make matters worse. A negative effect from a placebo is called a nocebo. A placebo that is given to a participant, and told it is a stimulant, will increase heart rate but a placebo given and told it is a depressant will have opposite effects. If you take something and are told that it will make you stronger then you will be stronger. The correlation between belief, perception and expectation dramatically change the effects of a given placebo. Perhaps most interesting is that the color of the pill also makes a difference. Bright colored placebo pills work better as stimulants and soft colored placebos as depressants. In short, how do placebos work? We don’t know, but the belief in, hence the brain, is at the core of placebo effectiveness.