The placebo effect refers to the phenomenon in which some people experience some type of benefit after the administration of a placebo. A placebo is a substance with no known medical effects, such as sterile water, saline solution or a sugar pill. In short, a placebo is a fake treatment that in some cases can produce a very real response. The expectations of the patient play an important role in the placebo effect; the more a person expects the treatment to work, the more likely they are to exhibit a placebo response.
In medical research, some patients in a study may be administered a placebo while other participants receive the actual treatment. The purpose of doing this is to determine whether or not the treatment has an actual effect. If participants taking the actual drug demonstrate a significant improvement over those taking the placebo, the study can help support the claim for the drug's effectiveness.
Examples of the Placebo Effect
For example, let's imagine that a participant has volunteered for a study to determine the effectiveness of a new headache drug. After taking the drug, she finds that her headache quickly dissipates and she feels much better. However, she later learns that she was in the placebo group and that the drug she was given was just a sugar pill.
Why Causes the Placebo Effect?
So why do some individuals experience changes even when they are only receiving a placebo? In our example above, one possible explanation is that taking the placebo triggered a release of endorphins. Endorphins have a structure similar to morphine and other opiate painkillers and act as the brain's own natural painkillers.
Researchers have been able to demonstrate the placebo effect in action using brain scans. In one study, participants had a hot, painful piece of metal placed on their hand and then received either a pain-killing drug or a placebo injection. In both cases, the subject reported that the injection helped reduce the pain. The researchers used positron emission tomography (PET) scans to look at each person's brain and found that areas of the anterior cingulate cortex, the area of the brain that contains many opiate receptors, were activated in both the placebo and treatment groups.
Other possible explanations include conditioning, motivation and expectation. In some cases, a placebo can be paired with an actual treatment until it actually comes to evoke the desired effect, an example of classical conditioning. People who are highly motivated to believe that a treatment will work may be more likely to experience a placebo effect.
Conversely, individuals can experience negative symptoms as a response to a placebo, a response that is sometimes referred to as the "nocebo effect". For example, a patient might report having headaches, nausea or dizziness in response to a placebo.
Hróbjartsson A, Norup M (June 2003). The use of placebo interventions in medical practice--a national questionnaire survey of Danish clinicians. Evaluation & the Health Professions 26(2), 153?65.
Petrovic, P., Kalso, E., Petersson, K. M., & Ingvar, M. (2002). Placebo and opioid analgesia: Imaging a shared neuronal network. Science, 295, 1737-1740.
Rajagopal, S. (2007). The nocebo effect. Priory.com. Found at http://priory.com/medicine/Nocebo.htm