According to Gibbs (2010), placebos are interventions that do not have a true treatment effect on the symptom or disease for which they are used. An important aspect is that people think they receive a true treatment.
Even though people receive no treatment, they may show a placebo effect. In short, a placebo effect is seen an alleviation of symptoms, despite the fact that people do not receive a treatment. In other words, the alleviation of symptoms must rely on other mechanisms than the treatment mechanisms (i.e., medicine).
The placebo effect may work through various psychological processes: classical conditioning; patient expectancy; the patient’s desire for a favorable treatment outcome. Often, there is seen a neurobiological or immunological basis for the placebo effect (Gibbs, 2010).
The placebo effect is therefore considered to be as “real” as a real treatment outcome. Sometimes, placebo effects elicit therapeutic effects that are equivalent to real treatment effects.
A placebo condition is used in clinical research for two main reasons. The first (1) is to ensure blinding procedures of both patients and researchers, i.e. double blind. The second (2) is to observe differences between the true treatment effect and the placebo effect (Gibbs, 2010).
For example, if there is no difference between the treatment group, and the placebo group, the treatment does not have a significant therapeutic effect.
The placebo effect may occur because something has changed the cognitive evaluation of whether or not to evoke a symptom.
For example, if you believe and expect that your symptoms improve, you change your cognitive evaluation of those symptoms, and in fact, symptoms may start to improve (the placebo effect). That is the power of the mind.