A placebo is an inactive substance, such as a pill, liquid, etc, that is given as if it was a therapeutic treatment, but which actually has no therapeutic value other than the “placebo effect.”

The placebo effect is also sometimes called the “subject-expectancy effect.” It is the phenomenon that symptoms can be alleviated by an otherwise ineffective treatment, since the patient expects or believes that it will work. Some people believe the placebo effect to be a remarkable aspect of human physiology, while others consider it to be an illusion arising from the way medical experiments were conducted. The phenomenon is not fully understood by science, but there has been clinical evidence of its presence.

Conversely, a patient who does not believe in a treatment may experience worsening of symptoms. This is called the “nocebo effect” and can be measured in the same way as the placebo effect. The patients receiving the placebo may nullify this effect by simply having a negative attitude toward the efficacy of the substance administered, which often leads to the nocebo effect. This outcome isn’t caused by the substance itself, but by the patient’s mentality toward his or her ability to get well.

Placebos were originally a substance that a well-meaning doctor would give to a patient, telling them it was a powerful drug when in actuality it was nothing more than a sugar pill. The subsequent reduction of the patient’s symptoms was attributed to their belief in the drug.

Placebos are not active themselves, but a patient may experience clinical effects while taking one. When a placebo is given to mimic a previously administered drug, the patient may experience the same side effects. Most of these are thought to be psychological in nature or due to other unrelated factors. A placebo involving ingestion, injection, or incision is often more powerful than a non-invasive technique. As well, placebos given by authority figures such as doctors and other experts may also have a more powerful effect.

Researchers normally use placebos in clinical trials, with a “test group” of patients receiving whatever therapy is being tested, and a “control group” receiving a placebo. It can then be determined if the results of the “test” group exceed those due to the placebo effect. If it does, it can be assumed the actual treatment was effective. If a therapy or medicine has no effect beyond the placebo, then it is said to have no effect or efficacy beyond non-specific effects.

Placebos cannot always be applied in studies because some drugs have clear physiological effects, and as such, a sugar pill would not be an effective placebo in these instances. In such cases, it is necessary to use a psychoactive placebo, i.e., a drug that produces enough physical side effects to be believed as the active drug.

Bioethicists have raised concerns about the use of placebos. Much of these have been incorporated into modern rules governing the use of such substances in research but some issues remain subject to debate.

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