Final answer:
A placebo is a fake treatment used in studies to control for the placebo effect, which causes psychological reactions in patients who believe they are being treated. The placebo effect can cause real symptom relief even though the placebo itself has no therapeutic properties.
Step-by-step explanation:
A placebo is a fake treatment that has no physiological effect on health. It is commonly used in clinical studies to control for the placebo effect, which is a psychologically based reaction to a treatment. Even though the placebo itself does not act on the condition being treated, patients may feel better simply because they believe they are being treated. For example, when testing a new medication for depression, researchers may create two groups: one that receives the actual medication and another that receives a placebo. Neither group knows which treatment they are receiving, to ensure that responses are due to the effect of the drug and not the participants' beliefs about the treatment.
The placebo effect can produce very real responses, such as relief from symptoms, even when the treatment has no active therapeutic effect. This effect has been observed across various conditions, including during a study by Schachter & Singer in 1962, where responses like itching feet or headache occurred in participants after receiving placebo injections, influenced by the behavior of confederates in the room.