Placebo: Effects, Examples, Types, and More



A placebo is something, such as a substance or procedure, that has no inherent ability to directly produce an effect of interest, but which can nevertheless produce this effect indirectly, generally through a psychological response. Most commonly, the term “placebo” is used in the medical context, to refer to an inert substance (e.g., a sugar pill) with no active ingredients or to a similar type of treatment, which leads to positive outcomes for patients (e.g., reduced pain) despite having no direct physiological effect.

Accordingly, the placebo effect (also referred to as placebo response) occurs when people experience a (usually positive) effect as a result of a substance or procedure that cannot directly produce that effect (i.e., a placebo), generally as a result of their psychological response to it.

The placebo effect can play an important role in various contexts, so it’s important to understand it. As such, in the following article you will learn more about placebos, understand how they work, and see how you can account for and use the placebo effect.


Examples of placebos and the placebo effect

A common example of placebos is placebo medication (e.g., sugar pills or saline injections), which have no active ingredients, but which can lead to a placebo effect, for instance by reducing the pain that people feel.

A related example of placebos is placebo surgery, which involves making it appear as if someone underwent a procedure (e.g., by cutting their skin), without actually completing the full procedure. This type of procedure can sometimes create a placebo effect, for example by leading to similar improvements in pain and mobility as certain types of real knee surgery.

Accordingly, placebos play a critical role in medical experiments and clinical trials, since the effectiveness of new treatments is often compared to the effectiveness of a placebo, to understand what portion of the treatment is attributable to the treatment itself.

In addition, the potential benefits of the placebo effect can explain why various treatments in alternative medicine, which have no inherent physiological effect, can make people feel better. For example, research suggests that when it comes to homeopathy, which is a widespread system of alternative medicine that involves the use of inert medicine (e.g., sugar pills), the improved outcomes that patients sometimes experience can be attributed to the placebo effect.

Finally, although placebos are most commonly associated with medicine, they exist in other domains in various forms. A common example of this that people often encounter in everyday life are placebo buttons, which don’t do anything when pressed, but are often placed in places such as crosswalks, elevators, and office thermostats in order to give people an illusion of control.


Types of placebos

Inactive (pure) vs. active (impure) placebos

An inactive (or pure) placebo is one that is considered inert, and therefore has no direct pharmacological effect. For example, sugar pills are often considered an inactive and pure placebo, since they do not directly influence a person’s physiology in any way, though they may influence them through the placebo effect.

An active (or impure) placebo is not considered inert, and can directly have a direct pharmacological effect, though not on the phenomenon of interest. For example, vitamin transfusions can be considered an active and impure placebo in the treatment of cancer, if they are not expected to influence it directly, though they may still influence a person’s physiology, as can antibiotics used for treating viral infections.

The concepts of inactive and active placebos are used primarily in the domain of medicine. Outside the context of medicine, they can be defined as having no direct effect, rather than no direct pharmacological effect in particular.

Active placebos can be important in cases where the use of an inactive placebo would make it obvious that a placebo is used, rather than something that has a direct effect. For example, this can be important for certain clinical trials, where the drug of interest has strong psychoactive effects, so patients will find it relatively easy to know if they were given an inert placebo.

However, the concept of active placebos has also been criticized, primarily because it’s not always clear that an impure placebo can’t actually influence the phenomenon of interest directly (i.e., whether it is truly a placebo). For example, even if a vitamin infusion isn’t expected to influence cancer directly, it can still have a non-placebo effect if the patient is vitamin deficient. Similarly, even if antibiotics aren’t expected to influence a viral infection, it’s not always clear in clinical settings if an infection is not caused, at least partly, by bacteria. This is an issue that can extend to inactive placebos, such as saline injections, which may be considered active in some circumstances, such as when they’re administered at a high enough dose to have a direct physiological effect on a phenomenon of interest.


Closed-label vs. open-label placebos

A closed-label placebo (also known as a hidden, concealed, or deceptive placebo) is a placebo that the person that it is administered to does not know is a placebo, or does not know for sure is a placebo. For example, if someone is given sugar pills and is told that the pills are antibiotics, that person is being given a closed-label placebo.

Conversely, an open-label placebo (also known as non-hidden, non-concealed, or non-deceptive placebo) is a placebo that the person that it is administered to knows is a placebo, because they are told so explicitly. For example, if someone is given sugar pills and is told that they are sugar pills meant to create a placebo effect, that person is being given an open-label placebo.

Placebos can sometimes work regardless of whether they are closed-label or open-label, which means that they can influence people even when those people know that they are being given a placebo. However, making a placebo open-label can influence its effectiveness, including by reducing it. Nevertheless, this may be balanced by other advantages, such as reducing the likelihood of interpersonal conflicts and trust issues that may occur when someone is given a placebo in a deceptive manner.


Positive vs. negative placebos (nocebos)

Placebos can be differentiated based on whether they lead to outcomes that are perceived as positive (e.g., beneficial to patients) or negative (e.g., harmful to patients). For example, a placebo that reduces pain may be considered positive, while a placebo that increases pain may be considered negative.

A negative placebo is sometimes referred to as nocebo, and correspondingly, a negative placebo effect can be referred to as a nocebo effect. It is sometimes also referred to as the anti-placebo effect, the reverse placebo effect, and the opposite of the placebo.


Other types of placebos

Placebos can also be categorized based on other criteria, such as:

  • Form. For example, this can involve differentiating between pharmacological placebos (i.e., those that are based on administering some substance, such as sugar pills), physical placebos (i.e., those that are based on some device, such as a machine without an electrical current), procedural placebos (e.g., sham surgery), and psychological placebos (e.g., suggesting that someone is going to feel better).
  • Outcome. For example, this can involve differentiating between placebos that are meant to alleviate pain, those that are meant to improve cognitive performance, and those that are meant to improve physical function.
  • Effectiveness. For example, this can involve differentiating between placebos that successfully elicit a placebo response in a certain situation, and those that do not.

Different placebos can work through different mechanisms and lead to different effects, even if they’re both given in a similar context (e.g., as a treatment for the same condition).

In addition, note that the term “placebo” can also be used in a more general sense, to refer to something that is done or given to satisfy someone, even though it is not what the person in question actually wants. For example, a company may make small and meaningless gestures as a placebo in response to employees’ demands to improve working conditions.


How placebos work

From a psychological perspective, there are various cognitive mechanisms that can broadly explain how placebos work. For example, according to expectancy theory, the placebo elicits an expectation for a particular effect within a person, and the expectation of this effect causes the person to experience the effect, or to believe that they are experiencing it. Alternatively, according to the theory of classical conditioning, the placebo serves as a stimulus that resembles a traditional medication or treatment, which the patient is conditioned to respond to by experiencing an improvement in their condition, based on their past experiences. Furthermore, other mechanisms may also play a role, such as that people are motivated to feel better, and the placebo effect helps them fulfill that motivation.

Different combinations of mechanisms may play a role in different situations, especially since there are many different types of placebos, that can be used in different ways, under different circumstances, and lead to different outcomes. Furthermore, various other mechanisms could also cause the placebo effect or be involved in it, including both cognitive and neurobiological ones, in both humans and in animals (who can also experience the placebo effect).

In addition, other factors can also influence the placebo effect. This includes personal factors, such as people’s somatic focus (i.e., their tendency to think about their symptoms), their suggestibility, and various aspects of their genetics. Furthermore, this also includes situational factors, such as the environment that a person is in when the placebo is administered and the way in which the placebo is administered.

A key situational factor the influences the effectiveness of placebos is the way they are presented. This means, for example, that the strength of the placebo effect can depend on the price of the placebo, so people experience a stronger effect if they are told that the placebo is more expensive, a phenomenon that is often utilized in marketing. Similarly, the effect of the placebo can be stronger if the ritual which is associated with it is extended, dramatized, or made more formal in some way.


Effects of placebos

Benefits of placebos

The placebo effect can lead to many positive outcomes, both in terms of subjective measures, such as reduced pain and nausea, and objective measures, such as bronchial hyperreactivity in asthma patients. These and similar benefits have been reported in the context of many medical conditions, such as osteoarthritis, fibromyalgia, rheumatology, allergies, depression, and anxiety.

Placebos are not always as effective as an active treatment in those cases, but placebos may nevertheless have certain advantages over an active treatment, such as potentially leading to fewer and less severe side-effects, or being less expensive.

In addition, placebos can have benefits outside the medical context, for example when it comes to improving cognitive or physical performance.

Note: the average strength of the placebo effect in clinical trials might be increasing over time in some domains, and this potential increase has been attributed to various potential causes, such as increased expectations from patients and increased enrollment of patients with minor illnesses in clinical trials.


Limitations of placebos

The placebo effect is limited in many ways, including:

  • The ways in which it can influence people (e.g., there are medical conditions that it can do nothing for).
  • The degree to which it can influence people (e.g., even if it helps alleviate someone’s pain, that doesn’t mean that it will eliminate the pain entirely).
  • The amount of time it can influence people for (e.g., because its influence may decrease over time).
  • The people it can influence (since some people are less disposed to experiencing it than others).
  • The situations in which it can influence people (e.g., because a factor such as stress may reduce placebo response in some cases).

As such, even though placebos can be beneficial, they should not be viewed as a perfect solution that’s guaranteed to always work or to solve issues fully.


Dangers of placebos

Placebos can lead to a number of potential issues, including:

  • A negative placebo response (i.e., nocebo response). This occurs when the placebo response leads to negative outcomes, such as increased pain.
  • A negative non-placebo response. This occurs when a placebo leads to negative outcomes that don’t have to do with the placebo response, such as when an active placebo causes headaches due to non-inert components that it contains.
  • Avoidance of necessary treatment. This occurs when a person chooses to use only a placebo in place of an alternative treatment that may be necessary or more beneficial.
  • Interpersonal issues. This occurs when the choice to give a placebo causes issues for relationships, for example because the person who was given a placebo finds out about it and feels deceived.

Some of these issues, such as interpersonal issues, are not inherent to placebos, but rather depend on factors such as how the placebo was administered, who administered it, and what was the purpose of administering it.

In addition, while these issues are potentially associated with placebos, none of them are guaranteed to occur in any given situation, meaning that it’s possible for people to benefit from a placebo without experiencing any of these issues.


Ethics of placebos

The use of placebos is controversial from an ethical perspective due to various potential issues, such as that giving a placebo to someone may violate their autonomy in some cases. Furthermore, the ethics of this, may depend on various factors, such as:

  • Whether there is deception or concealment involved in the placebo (e.g., whether the person knows that they’re being given a placebo or not).
  • Whether the person in question has consented to receive a placebo.
  • The reason for administering the placebo (e.g., because it’s likely to help the patient or because it can save money).
  • The outcomes that the placebo can to compared to alternative treatments.

Accordingly, different types of placebos may be perceived differently from an ethical perspective. For example, an open-label placebo, given to someone who knows that it’s a placebo, may be perceived differently than a placebo that is given to someone who doesn’t know that it’s a placebo. Similarly, a placebo that is administered to a control group as part of a clinical trial may be perceived differently than a placebo that is administered to a regular patient.

Note: the use of placebos to help people, especially when there is an element of concealment involved, is often considered a form of paternalism, and has received much criticism on ethical grounds.


How to use placebos

To use a placebo effectively, you should consider the following questions, which will help you determine whether you should use a placebo in the first place, and if so then how:

  • What are your goals for using the placebo? For example, are you trying to make someone feel better, or are you trying to establish a point of comparison to see whether an alternative treatment has a non-placebo pharmacological effect?
  • Who will you be giving the placebo to? For example, will you be administering it to yourself, or to someone else? When considering this, make sure to also consider the relevant attributes of the person that you’ll be administering the placebo to, such as their suggestibility.
  • What are the potential benefits and harms of using a placebo in this case, and how do they compare to each other? This is crucial both for determining whether using a placebo is the right thing to do, and for identifying potential issues that you should be prepared to address if you use it. When considering this, make sure to also consider the ethics of using the placebo, as well as indirect harms that the placebo may lead to, such as interpersonal conflicts and a failure to address underlying problems in the long term.
  • Are there any potential alternatives to a placebo in this case, and if so, then how do they compare to the placebo in terms of factors such as effectiveness, risk, and cost? For example, this can be relevant when considering whether you should give someone a placebo or an active treatment.
  • What placebos can you use, and how do they compare to each other? For example, consider whether it would be better to use a pharmacological placebo (e.g., sugar pills) or a psychological one (e.g., telling someone that they’re going to feel better soon), and whether it would it be better to use an inactive placebo or an active one.
  • How can you use your preferred placebo in a way that’s as effective as possible? For example, consider how can you present the placebo in a way that will increase its effectiveness (e.g., by making it appear expensive or by associating it with an elaborate ritual). Similarly, consider if it would be better to be open that what you’re administering is a placebo and to explain the rationale behind it, or to hide the fact that it’s a placebo, either initially or in general. In addition, consider when and where you should administer the placebo, to further maximize its effectiveness.


Pointing out and reducing the placebo effect

When people are unaware that something is a placebo, it can sometimes be beneficial to point this out, which will likely reduce the associated placebo effect. This can be relevant, for example:

  • If someone is relying on a placebo to deal with some issue, and the placebo isn’t actually solving this issue, even though it feels to them like it does.
  • If someone is spending large amounts of money on an expensive but unnecessary placebo.
  • If someone is being deceived into thinking that something isn’t a placebo.
  • If the placebo can lead to dangerous side effects.
  • If there are substantially better alternatives available to the placebo.
  • If the placebo is causing negative effects, such as increased stress (i.e., if the placebo is acting as a nocebo).

However, various considerations can influence whether you should point out and reduce the placebo effect. For example, even if someone is being deceived into thinking that something isn’t a placebo, that could be reasonable if they’re part of a clinical trial, and have given proper consent.

In addition, it’s important to be cautious before choosing to reduce someone’s placebo effect, and to properly weigh the pros and cons of doing so. For example, if a certain placebo helps someone feel calm because they think that it’s “real” medicine, and the placebo itself is safe and inexpensive, then it might be better to avoid mentioning that it’s a placebo, because otherwise you could cause more harm than good.


Accounting for the placebo effect

It can sometimes be useful to account for the placebo effect even in cases where you don’t influence this effect directly. For example, this can help you understand why someone’s behavior changes after they receive a placebo, or can help you predict that this will happen.


Summary and conclusions

  • A placebo is something, such as a substance or procedure, that has no inherent ability to directly produce an effect of interest, but which can nevertheless produce this effect indirectly, generally through a psychological response.
  • Most commonly, the term “placebo” is used in the medical context, to refer to an inert substance (e.g., a sugar pill) with no active ingredients or to a similar type of treatment, which leads to positive outcomes for patients (e.g., reduced pain) despite having no direct physiological effect.
  • Placebos can influence both subjective outcomes, such as pain perception, and objective outcomes, such as physical mobility, though their benefits are often limited, so they shouldn’t be viewed as a perfect solution to all problems.
  • Placebos can affect people through various mechanisms, including people’s expectation that the treatment will help them, people’s conditioned response to treatments based on their past experiences, and people’s desire for the treatment to work, and placebos can sometimes work even when people know that they’re given a placebo.
  • To use a placebo effectively, you should consider questions such as what are your goals, who will you be giving the placebo to, what are the potential benefits and harms associated with the placebo, and what alternatives are available to it.