The placebo effect is the phenomenon whereby a patient's symptoms can be alleviated by an otherwise ineffective treatment; most likely because the individual expects or believes that the treatment will work. The placebo effect is actually a generic term for various effects that cause people to reinterpret their illness or symptoms
The placebo effect is a psychological response to treatment. Physical conditions do not improve with placebos. Placebos do not cure, as many people mistakenly believe; it is the perceived improvement of symptoms that characterizes the placebo effect.
It should be noted that all medicines induce the placebo effect. It is only those treatments that have an effect above and beyond that produced by a placebo that are classed as efficacious.