The Placebo Effect

Key Terms

Placebo: a faux substance or treatment given to a patient in lieu of real medicine.

Double-blind experiment: an experiment in which neither the researcher nor the participants know which patients are receiving the placebo and the real treatment. 

The Nocebo Effect: While the placebo effect usually refers to patients reporting positive improvements in their wellbeing without receiving any real treatment, nocebo occurs when people report side-effects or worsening conditions even though they had only taken a placebo.2


Before advances in science and technology, it was very difficult to determine why different medicines and substances cured illnesses. People could only hypothesize that something was happening inside our bodies that was leading to positive change — but really, it could have been the placebo effect all along.

The first scientific demonstration of the placebo effect ocurredin 1799. John Haygarth, a British physician, set out to disprove the commonly held belief that expensive metal rods, when stroked over the body, would cure individuals of disease. Elisha Perkins, a physician, had put forward this electromagnetic cure to disease and sold the metal rods, known as tractors, for a hefty price.3 Haygarth sensed that something wasn’t right and decided to give individuals fake, wooden tractors that looked the same as the original ones, and found that 4 out of 5 patients reported that their pain improved. Haygarth realized the mere suggestion of receiving a treatment can help people feel better.4

The term placebo was first introduced in the 18th century in Hooper’s Medical Dictionary with the definition: “any medicine adopted to please rather than to benefit the patient.5 A placebo referred to the substance or treatment in question, while the placebo effect was the resulting improvement in wellbeing that resulted from taking the placebo. 

It wasn’t until years later, in 1920, that the placebo effect was coined and people began to take serious note of its power. While treating World War II soldiers, American anesthesiologist Henry Beecher found that men - who had not received any morphine but were badly hurt in battle - did not report feelings of pain, despite their bones being shattered and their skin shredded. Beecher hypothesized the soldiers were so elated they had survived that their euphoric state overrode physiological feelings of pain.5

Treating wounded soldiers sparked Beecher’s interest in the placebo effect and he dedicated the rest of his career to studying it at Harvard Medical School. In 1955, Beecher published a landmark paper, “The Powerful Placebo”, which changed the medical field immensely. In this paper, he outlined findings from 15 clinical trials where he had compared control groups that received placebos to other patients who had ingested the real medicine. He reported that in 35% of cases, pain, nausea, and anxiety was satisfactorily relieved by a placebo. He did not think people were making it up that they felt better, but that the placebo had a kind of therapeutic effectiveness.6

“The Powerful Placebo” was cited almost a thousand times in scientific journals and for around 40 years, it went unchallenged. It also changed scientific procedure by making double-blind clinical trials the gold standard.

Today, the placebo effect is still widely believed, but people are more skeptical. Much of this skepticism comes from not understanding how the placebo effect works. How can feeling better mentally help us feel better physically? There are a few theories:

  • Hormones: Feeling good produces hormones known as endorphins. Endorphins are like the brain’s own natural painkillers that make us feel better. So if we believe we are receiving a substance that will improve our pain, our brain could be tricked into releasing endorphins, which end up actually making us feel better!2
  • Conditioning: It could be that the association of a substance with feeling better is why we feel better. If someone is used to taking painkillers to help relieve their headaches, they have been conditioned to associate the two together and will likely still feel better if they are given a placebo that resembles the painkiller.2
  • Expectations: It could be as plain and simple as the fact that our positivity helps us feel better. Many studies have linked happiness to being healthier, so expecting that we will get better might be enough to make us feel better. These expectations can be created through behavioral or social cues. Behaviorally, we expect to feel better if we take a pill. Socially, we expect to feel better if our doctor tells us the treatment we are receiving will make us feel better.2 Our expectations might also influence our perception of how we feel due to the confirmation bias. When we are told a substance is supposed to make us feel better, we are more likely to pay attention to feelings that confirm this belief.7


The placebo effect has both positive and negative side effects. On the one hand, if someone can feel better without needing to take medicine or undergo a treatment, then we’re all for the placebo effect! It can help us understand the link between our psychology and our physiology and remember that mental health is vital to our overall well being. As pain researcher Jeffrey Mogilhas claimed, the placebo effect is “at the precise interface of biology and psychology.” 7 Even if it doesn’t cure diseases, it might help with other issues like depression, pain management, or symptom relief.2

On the other hand, the placebo effect is dangerous if people aren’t actually getting any better, but thinking they are. Patients might stop their search for treatment beyond taking the placebo, which might only have surface-level effects on their health. Additionally, pain can actually be really important. Those wounded soldiers who were badly injured might try engaging in activity that worsens their condition because a lack of pain leads them to think they are fine. 


Not everyone agrees that the placebo effect is real. In the1990s, people began to question Beecher’s work and the ethical nature of double-blind clinical trials. Critics began to point out that Beecher’s evidence was tainted by errors and misunderstandings, but it was difficult to change public opinion.6

There is also debate on what exactly leads to an improved feeling after taking a placebo. Is there actually a physiological change that occurs because our brains are tricked, or do we only feel better psychologically?

Others chalk up the placebo effect to the observer-expectancy effect. The effect describes a phenomenon where people’s behavior is influenced by their perceived expectations of an observer. Individuals involved in medical experiments are likely to believe that researchers and doctors are expecting them to feel better, and therefore, they might report feeling better even if they don’t, in order to meet those expectations. 

The controversies surrounding the placebo effect don’t only surround its validity, but also whether or not it’s ethical. Vitamins, hair pills, and skin products are advertised to help fix all our biological blemishes - is it right to make people spend hundreds of dollars on products that might only have a therapeutic effect? Experimental medical trials are often a last resort for terminal patients, a final beacon of hope that they will get better. Is it fair that half of the patients in the medical trial are given a fake substance or treatment?

Alcohol & the Placebo Effect

With alcohol-free beer and wine becoming more popular these days, it is interesting to consider whether the placebo effect can make people feel tipsy even if they are not ingesting any alcohol. If an individual is unaware that their drink is alcohol-free, will they still exhibit alcohol-related behavior such as looser inhibitions or loss of memory because they associate alcohol with these behaviors? 

According to two psychologists in New Zealand, Seema Assefi and Maryanne Garry, this can be the case. The researchers found that memory was indeed affected by an alcohol placebo.8 

Their study recruited 148 students and split them into two groups. One group was told that they would be receiving vodka and tonic drinks, while the other group was told they were being given tonic water. All participants were actually drinking plain tonic water. To make the study more realistic, it was carried out in a bar-like room and included props like alcohol bottles and bartenders. All drinks were poured from sealed vodka bottles, so that those who were told they were receiving vodka were likely to believe it.8

After having their drinks, participants were asked to watch a slideshow depicting a crime. They then read a summary of the crime that included misleading information. When asked about the crime, Assefi and Garry found that those who thought they drank vodka tonics were more inaccurate in their eyewitness testimonials. Just the mere suggestion that they drank alcohol made their memory worse!8

Individuals who had been told they were drinking alcohol even showed physical behaviors relating to drunkenness, such as excessive giggling, swaying, and/or flirting. The participants were shocked to hear they had all received tonic water.8

Assefi and Garry’s study shows that our behavior is influenced a lot by our mind and that mere suggestion has a powerful effect on our physical behavior.8

COVID-19 Clinical Trials

To ensure the efficacy of COVID-19 vaccines, companies conducted double-blind clinical trials. Since the COVID-19 pandemic was affecting the world on a grand scale, the studies reraised ethical concerns of double-blind clinical trials. 

For this reason, the World Health Organization developed recommendations that mitigate these competing ethical and practical priorities.9 They recommended that the studies did not include individuals who were at greater risk of contracting the virus, such as healthcare workers, as they should receive the protection as soon as possible. Similarly, they recommended that individuals over the age of 65 who are more likely to experience serious symptoms if they contract the virus, should not be part of double-blind studies. They also suggested people should have the opportunity to partake in unblind studies so that they can make informed decisions about whether they would like to be involved.9

Related TDL Content

Mistruth Can Set You Free: The Power of (False) Belief

Taking a placebo can at the very least make you feel psychologically that you are feeling better. Even if the disease or injury persists, is there harm in the therapeutic effect of a placebo? In this article, our contributor Jeremy Koloski examines the positive and negative power of belief in multiple areas including medicine and religion.

I Think I Am, Therefore I Am

A popular theory behind the placebo effect rests in the idea that expectations have a profound effect on our lives. Similarly, the Pygmalion effect describes situations where people’s high expectations of us cause us to behave in ways that meet those expectations. In this article, our contributor Andrew Lewis discusses the psychology behind the “fake it till you make it” advice and gives guidance for how it can be applied to succeed in the workplace.


  1. Placebo Quotes. (n.d.). Goodreads. Retrieved November 25, 2021, from
  2. Cherry, K. (2021, April 25). What Is the Placebo Effect? Verywell Mind.
  3. Watts, G. (2005, January 5). Histories: Elisha Perkins and his 'medical tractors'. New Scientist.
  4. Mestel, R. (2020, October 29). The imagination effect: A history of placebo power. Knowable Magazine.
  5. Gross, L. (2017). Putting placebos to the test. PLOS Biology, 15(2), e2001998.
  6. Barrowman, N. (2020, September 26). The Myth of the Placebo Effect. The New Atlantis.
  7. Resnick, B. (2017, July 7). The weird power of the placebo effect, explained. Vox.
  8. Whitehouse, D. (2003, July 1). Fake alcohol' can make you tipsy. BBC News.
  9. Singh, J. A., Kochhar, S., Wolff, J., Atuire, C., Bhan, A., Emanuel, E., Faden, R., Ghimire, P., Greco, D., Ho, C., Moon, S., Shamsi-Gooshki, E., Touré, A., Thomé, B., Smith, M. J., & Upshur, R. E. (2021). Placebo use and unblinding in COVID-19 vaccine trials: Recommendations of a WHO expert working group. Nature Medicine, 27(4), 569-570.

About the Authors

Dan Pilat's portrait

Dan Pilat

Dan is a Co-Founder and Managing Director at The Decision Lab. He is a bestselling author of Intention - a book he wrote with Wiley on the mindful application of behavioral science in organizations. Dan has a background in organizational decision making, with a BComm in Decision & Information Systems from McGill University. He has worked on enterprise-level behavioral architecture at TD Securities and BMO Capital Markets, where he advised management on the implementation of systems processing billions of dollars per week. Driven by an appetite for the latest in technology, Dan created a course on business intelligence and lectured at McGill University, and has applied behavioral science to topics such as augmented and virtual reality.

Sekoul Krastev's portrait

Dr. Sekoul Krastev

Sekoul is a Co-Founder and Managing Director at The Decision Lab. He is a bestselling author of Intention - a book he wrote with Wiley on the mindful application of behavioral science in organizations. A decision scientist with a PhD in Decision Neuroscience from McGill University, Sekoul's work has been featured in peer-reviewed journals and has been presented at conferences around the world. Sekoul previously advised management on innovation and engagement strategy at The Boston Consulting Group as well as on online media strategy at Google. He has a deep interest in the applications of behavioral science to new technology and has published on these topics in places such as the Huffington Post and Strategy & Business.

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