A placebo is an ineffectual medical treatment or procedure designed with the express intention of deceiving a patient or a participant of an experiment.
Although, at first glance, this might seem like an unprofessional and, perhaps, pointless thing to do, it is quite the reverse. Placebos are essential in the design of reliable clinical trials, and their surprising effect has become the focus of many studies.
The placebo effect refers to the impact that a placebo has on an individual. In other words, even an inert and inactive treatment can produce a measurable, positive health response. This outcome may fly in the face of common sense but it has been repeatedly demonstrated.
In this article, we will look at what the placebo effect entails, when it works, how it can be manipulated and when it is used in clinical settings.
Contents of this article:
Fast facts on placebos
Here are some key points about placebos. More detail and supporting information is in the main article.
- The placebo effect has been measured in thousands of medical experiments over the years
- Many doctors admit to regularly prescribing placebos
- The opposite of a placebo - generating a negative rather than a positive outcome - is a nocebo
- Drug companies must show that their new drugs work better than a placebo before they are released
- The color of a tablet can alter how strong its placebo effect is
- Larger pills induce a stronger effect than smaller pills
- Placebo comes from the Latin meaning "I will please"
- The exact mechanisms by which placebos work are still not known
- Some believe the self-healing properties of the placebo effect can be explained by evolutionary biology.
What is the placebo effect?
Placebo groups in clinical trials are essential to prove a new drug's efficacy.
The placebo effect describes any effect, psychological or physical, that a placebo drug (or intervention) has on an individual. The placebo has become an essential component of all good clinical trials.
In the early days of clinical trials, the capabilities of a new drug were simply measured against a group of people who took no medication at all.
However, since the discovery that the simple act of taking an empty tablet can produce the placebo effect, it is now considered essential to have a third group of participants. This additional group take a tablet containing no active ingredient (a sugar pill, for instance) to measure the response against them.
For a pharmaceutical company to bring a new drug to market, they must prove that it has a greater effect than taking nothing, but also that it has a greater effect than a placebo.
Placebos have been shown to produce measurable, physiological changes such as an increase in heart rate or blood pressure. However, it is illnesses that rely on self-reporting of symptoms to measure them that are most strongly influenced by placebos, such as depression, anxiety, irritable bowel syndrome (IBS) and chronic pain.
Placebo interventions vary in strength depending on many factors. This is quite an odd concept when one considers that no placebos contain any active components. For instance, an injection invokes a stronger placebo effect than a tablet. Two tablets work better than one, capsules are better than tablets and the bigger the pill, the better.
One review of multiple studies found that even the color of pills made a difference to the placebo results:
"Red, yellow, and orange are associated with a stimulant effect, while blue and green are related to a tranquilizing effect."1
Interventions such as sham acupuncture - using retractable needles that do not pierce the skin - have been repeatedly shown to be just as effective as acupuncture.2-4
To add another dimension to the strange and powerful placebo mystery, its effect varies between cultures. In treating gastric ulcers, the placebo effect is low in Brazil, higher in northern Europe and particularly high in Germany. However, the placebo effect in treating hypertension is lower in Germany than elsewhere.7
Examples of placebo effects
Placebos have shown to be effective in treating a number of conditions and illnesses.
Initially, placebos were only used in experiments as a control, but because of their startling abilities they have now been studied extensively in their own right.
The following conditions have been shown to respond well to the placebo effect:
- Pain: a placebo's ability to reduce pain is referred to as placebo analgesia. It is believed to work in one of two ways; either the placebo initiates the release of natural painkillers (endorphins), or they change the patient's perception of the pain.
Additionally, genuine analgesics have been found to be more effective if the patient knows they are being given the drugs, rather than the drug being given surreptitiously. In this case, the placebo effect can be viewed as assisting a genuine intervention8
- Depression: a substantial amount of the effect of antidepressants is believed to be reliant on the placebo effect. One review of eight studies found that even over a 12 week period, placebo antidepressants were effective, demonstrating the potentially long-lasting impact of placebos9
- Anxiety disorders: the placebo effect is particularly prevalent in trials for anti-anxiety drugs and significantly interrupts the discovery and trials of new forms of medication10
- Coughs: a review of trials into cough medication found that "85% of the reduction in cough is related to treatment with placebo, and only 15% attributable to the active ingredient"11
- Erectile dysfunction: in one study, participants were split into three groups. The first group was told they would receive a treatment for erectile dysfunction, the second group were told they would receive either a placebo or an actual treatment and the third group were told they would receive a placebo.
All three groups were, in fact, given placebo starch tablets, but all three groups' erectile dysfunction improved significantly without any significant differences between the three groups12
- IBS: a meta-analysis found that the placebo response rate ranged from 16.0% to 71.4%. It was also noted that the placebo effect is larger in trials where the participants are required to take medication less frequently, and individuals with lower anxiety levels appear to be more susceptible to the placebo effect.13
A more caring approach from clinicians was found to enhance the placebo effect.14 Interestingly, another trial found that even when the participants were aware they were taking a placebo, their IBS conditions improved15
- Parkinson's disease: a review of 11 clinical trials found that 16% of participants in the placebo groups showed significant improvements, sometimes lasting for 6 months.16 The effect seems to be due, at least in part, to dopamine release in the striatum17
- Epilepsy: defined as a 50% decrease in their normal seizure frequency, participants in anti-epilepsy drug trials have a 0-19% placebo response.18
On the next page, we look at how placebos work and their usage in clinical settings.