The placebo effect: how expectation changes what you feel

By Joanna · Published 27 October 2026

The placebo effect is the difference that expectation makes to how you feel, meaning a real change in reported symptoms or experience that comes from what you believe about a treatment, not from anything active in it. Its most surprising finding is that it can still work when people are told outright that their pill is inert.

Key takeaways

• A placebo looks like a real treatment but has no active ingredient, and the placebo effect is the difference between taking it and taking nothing.
• Placebos can change how symptoms such as pain and nausea feel, but a 2010 review found they do not appear to change the underlying disease.
• In a 2010 trial, 59% of people who knowingly took "sugar pills" reported adequate relief after three weeks, against 35% of people who took nothing.
• Expectation shapes ordinary experience too: in a 2008 study, the same wine tasted better, and lit up a pleasure-linked brain region more, when people were told it was expensive.
• The nocebo effect is the reverse: expecting harm can make people feel worse.

What is the placebo effect?

A placebo is something that looks like a real treatment but has no active ingredient, such as a sugar pill. The placebo effect is the difference between how people do after taking it and how they do with no treatment at all, which is why medical trials compare a new drug with a placebo instead of with nothing.

Researchers study the effect in its own right because it shows how much of what we feel depends on what we expect.

Is the placebo effect real?

Yes, within limits that matter, and according to the research summarised in Wikipedia's article on placebo , placebos can affect outcomes such as pain and nausea, which are things people feel and report. A 2010 Cochrane review found no important clinical effects of placebo in general and concluded that placebos do not appear to affect the disease itself.

So the honest summary is that the effect is real in experience and limited in biology. A placebo can change how a headache feels while doing nothing to what caused it, and that is why it is never a substitute for treatment.

How does the placebo effect work?

Researchers point to two main routes, expectation and conditioning. The psychologist Irving Kirsch described the first in 1985 as response expectancy: expecting to feel a certain way helps bring that feeling about. Conditioning works through experience, so a pill or a routine that has been followed by relief before can come to trigger some of that relief on its own.

The details of a treatment change the size of the effect. Taking more pills tends to strengthen it, injections tend to be stronger than capsules, and a doctor who is warm and expects the treatment to work makes the placebo more effective. Some researchers also suggest that carrying out a ritual, such as taking a pill at the same time every day, may matter more over time than believing in it.

What is open-label placebo?

Open-label placebo means giving someone a placebo and telling them it is one. It is easy to assume a placebo only works if the patient is fooled, and a 2010 trial led by Ted Kaptchuk put that assumption to a test.

The team recruited 80 adults with irritable bowel syndrome. Thirty-seven were given pills described to them as "made of an inert substance, like sugar pills", to take twice a day, with an explanation that such pills had helped other people through mind-body processes. The other 43 received no pills, and both groups had about the same amount of time with the researchers. After three weeks, 59% of the open-label group reported adequate relief, compared with 35% of the group that took nothing, and the difference in overall improvement was statistically significant. You can read the full study in PLOS ONE .

The authors called it a pilot, because the trial was small and short, could not be double-blinded, and measured symptoms that patients report themselves, and they asked for larger studies. Later work has broadly held up: a 2021 analysis of 11 open-label trials found a significant effect, slightly smaller overall, and described the field as still in its infancy.

Does expectation change everyday experiences too?

Yes, and one of the neatest demonstrations has nothing to do with medicine. In a 2008 study published in PNAS, researchers scanned people's brains while they tasted wines described at different prices, without telling them that some of the "different" wines were the same wine. When a wine was presented as more expensive, people rated it as more pleasant, and activity rose in the medial orbitofrontal cortex, a brain region linked to how pleasant an experience feels. The study's record at Caltech has the details.

Nothing about the wine changed between tastings, only what people expected from it, and that expectation showed up both in what they said and in the brain region linked to enjoyment.

What is the nocebo effect?

The nocebo effect is the placebo effect in reverse: expecting harm can make people feel worse, or report new symptoms, even from something inert.

Can you use the placebo effect on yourself?

Not as a treatment, and not instead of care. The 2010 trial gave its placebos inside a clinic, with researchers explaining them and the same follow-up for both groups, and it measured symptoms people report, not disease. If something is wrong with your health, the placebo effect is a reason to see a doctor who explains things well, not a reason to skip one.

What you can take from the research is how much expectation colours experience. The same wine tastes different with a different price on it, and a warm, confident doctor makes a placebo work better. Noticing what you expect from a day, a task or yourself is a fair place to start, and our guide to self-concept looks at the expectations people carry about who they are.

Frequently asked questions

Does a placebo only work if you are fooled? No. In the 2010 open-label trial, people who were told their pills were inert still reported more relief than people who took nothing, and later trials have found a smaller but significant effect.

Can a placebo cure an illness? No. A 2010 Cochrane review found that placebos do not appear to affect the disease itself, even when they change how symptoms such as pain feel.

Is the placebo effect all in your head? It is in how you feel, which is real to the person feeling it. Expectation changed both what people reported and their brain activity in the wine study, but it does not change the cause of an illness.

What is the difference between placebo and nocebo? A placebo effect is feeling better because you expect to, and a nocebo effect is feeling worse because you expect to.

Why do injections work better than pills as placebos? Injections tend to produce stronger placebo effects than capsules, and taking more pills strengthens the effect too. Both fit the idea that what a treatment looks like shapes what people expect from it.

What expectation can and cannot do

The placebo effect is one of the clearest demonstrations that what you expect changes what you feel, and open-label placebo shows it does not even need anyone to be fooled. It also has firm edges: it moves experience and reported symptoms, not disease. Holding both of those at once is the most useful way to understand it.

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