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The placebo effect: why it matters in wellness research
The placebo effect is real but mostly modest, changing how people feel more than what tests measure, so wellness claims need placebo-controlled trials.
The placebo effect is the improvement people report after a treatment that has no active ingredient, driven by expectation, attention and the ritual of being treated. It matters in wellness research because it can make an inactive product look as if it works, which is why fair tests compare a treatment against a placebo rather than against nothing.
That does not mean placebos are magic, or that they do nothing. The best evidence points to something in between: modest, real changes in how people feel, mostly in symptoms they rate themselves, such as pain and nausea, and very little effect on things a machine or a lab test measures.
How big is the placebo effect, really?
Most studies cannot answer this, because they compare a treatment with a placebo, not a placebo with nothing at all. In 2001 two Danish researchers, Asbjørn Hróbjartsson and Peter Gøtzsche, gathered the trials that did include a no-treatment group. Writing in the New England Journal of Medicine, they analysed 114 trials with usable data and found that placebo had no significant effect on yes-or-no outcomes, such as whether someone recovered. It had a small benefit on continuous, self-reported measures. In 27 pain trials it lowered pain by about 6.5 mm on a 100 mm scale.
Their 2010 Cochrane update was larger: 234 included trials covering 60 clinical conditions. The conclusion held. Placebo interventions did not have important clinical effects in general, but they could influence patient-reported outcomes, especially pain and nausea. The authors also found larger placebo effects in small trials and in trials using physical placebos such as sham acupuncture, and noted that it is hard to separate a true placebo effect from biased reporting.
Is feeling better the same as getting better?
Not always, and a 2011 asthma study in the New England Journal of Medicine shows the gap clearly. Researchers in Boston gave 46 people with asthma, in random order, a real albuterol inhaler (the same drug is called salbutamol in the UK), a dummy inhaler, sham acupuncture and no treatment, repeated over 12 visits. Among the 39 who finished, the real inhaler improved lung function, measured as FEV1, by 20%, against about 7% for each of the other three options.
The patients' own ratings told a different story. They reported 50% improvement with the real inhaler, 45% with the dummy inhaler and 46% with sham acupuncture, compared with 21% after no treatment. People felt almost as much better on a placebo as on the drug, while their airways had not changed. The authors concluded that patient self-reports can be unreliable when judging whether a treatment works.
Can surgery be a placebo?
Yes, and one of the most cited examples involves the knee. In a 2002 trial, also in the New England Journal of Medicine, 180 people with knee osteoarthritis were randomly assigned to arthroscopic débridement, arthroscopic lavage, or a placebo operation. In the placebo group, surgeons made skin incisions and simulated the procedure without inserting the arthroscope. Neither the patients nor the people assessing them knew which they had received.
Over two years, neither real procedure produced less pain or better function than the fake one. Without the placebo arm, the improvement patients reported after real surgery would easily have been credited to the operation itself.
Is the placebo effect all in the mind?
Not in the sense of being imaginary. A 1978 study in The Lancet gave naloxone, a drug that blocks the body's own opioids, to people recovering from wisdom tooth surgery. Naloxone increased pain in those who had responded to a placebo, but not in those who had not. The authors concluded this was consistent with endorphin release driving placebo pain relief.
The context of care matters too. In a 2008 BMJ trial, 262 adults with irritable bowel syndrome (IBS) were put on a waiting list, given sham acupuncture with minimal interaction, or given sham acupuncture by a warm, attentive and confident practitioner. After three weeks, adequate relief of symptoms was reported by 28%, 44% and 62% respectively. The researchers found the patient-practitioner relationship was the strongest component of the effect.
Can a placebo work if you know it is a placebo?
Possibly, at least for symptoms people rate themselves. In a 2010 trial published in PLoS One, 80 people with IBS received either pills openly described as placebo, made of an inert substance like sugar pills, or no treatment, with the same quality of contact with staff. After three weeks, the open-label placebo group reported significantly greater global improvement. It was a small, single-centre, three-week study with self-reported outcomes, so it is a reason for more research rather than proof.
What is the nocebo effect?
Expectation can make people feel worse as well as better. This is called the nocebo effect. The UK SAMSON trial, published in the Journal of the American College of Cardiology in 2021, recruited 60 people who had stopped taking statins because of side effects. Each received 12 monthly bottles in random order: four containing a statin, four a placebo and four empty.
Among the 49 who completed the year, average symptom scores were 8.0 in empty-bottle months, 16.3 in statin months and 15.4 in placebo months, with no significant difference between statin and placebo. Six months after the trial, half of the 60 participants were taking statins again. The symptoms were real. Most of them came from the act of taking a tablet, not from what was in it.
Why do wellness claims need placebo-controlled trials?
Put these findings together and a pattern emerges. The outcomes most open to placebo effects are the ones measured by asking people how they feel, and those are exactly the outcomes many wellness products promise to change. A product tested with no control group, or only against doing nothing, can look effective for reasons that have nothing to do with what is in it.
When you read a study behind a wellness claim, these questions help separate a real effect from a placebo response:
- Was there a placebo or sham group, not just a before-and-after comparison?
- Were participants and assessors blinded, so that neither knew who received what?
- Was the main outcome measured objectively, or only self-reported?
- Was the trial reasonably large? The 2010 Cochrane review found bigger placebo effects in small trials.
- Did the treatment beat the placebo group, or only the participants' starting point?
A treatment that only beats doing nothing has not shown that it beats the ritual of being treated. That is the comparison that counts.
This article is for education about research methods only. It is not medical advice, so speak to a qualified health professional about any treatment decision.
Frequently asked
- What is the placebo effect in simple terms?
- The placebo effect is the improvement people report after a treatment with no active ingredient, driven by expectation, attention and the ritual of being treated. Large reviews comparing placebo with no treatment, including a 2010 Cochrane review of 234 trials, found it mostly affects self-reported symptoms such as pain and nausea, with little effect on objective measures.
- Is the placebo effect real or just in people's heads?
- It is real in the sense that people genuinely feel different, and a 1978 Lancet study suggested placebo pain relief involves the body's own endorphins. But feeling better is not always getting better. In a 2011 asthma trial, a dummy inhaler made patients feel almost as improved as the real drug, while only the real drug improved lung function.
- Can a placebo work if you know it is a placebo?
- Possibly, for symptoms people rate themselves. A 2010 trial of 80 people with irritable bowel syndrome found that pills openly described as placebo led to greater reported improvement than no treatment over three weeks. It was small, short and relied on self-reported outcomes, so it supports further research rather than proving the effect.
- What is the nocebo effect?
- The nocebo effect is when expectation makes people feel worse, for example by producing side effects from an inactive pill. In the UK SAMSON trial, people who had stopped statins reported similar symptom scores in placebo months and statin months, and both were roughly double the scores in months when they took nothing.
- Why do wellness studies need a placebo group?
- Without one, any improvement could come from expectation, attention or the ritual of treatment rather than the product. A 2002 knee surgery trial found real operations did no better than a simulated one. Because wellness products usually target how people feel, a blinded placebo comparison is the fairest way to test them.
The studies and sources behind this page
- Hróbjartsson A, Gøtzsche PC. Is the placebo powerless? An analysis of clinical trials comparing placebo with no treatment. N Engl J Med 2001;344:1594-602.
- Hróbjartsson A, Gøtzsche PC. Placebo interventions for all clinical conditions. Cochrane Database Syst Rev 2010;(1):CD003974.
- Wechsler ME, Kelley JM, Boyd IO, et al. Active albuterol or placebo, sham acupuncture, or no intervention in asthma. N Engl J Med 2011;365:119-26.
- Moseley JB, O'Malley K, Petersen NJ, et al. A controlled trial of arthroscopic surgery for osteoarthritis of the knee. N Engl J Med 2002;347:81-8.
- Levine JD, Gordon NC, Fields HL. The mechanism of placebo analgesia. Lancet 1978;2:654-7.
- Kaptchuk TJ, Kelley JM, Conboy LA, et al. Components of placebo effect: randomised controlled trial in patients with irritable bowel syndrome. BMJ 2008;336:999-1003.
- Kaptchuk TJ, Friedlander E, Kelley JM, et al. Placebos without deception: a randomized controlled trial in irritable bowel syndrome. PLoS One 2010;5:e15591.
- Howard JP, Wood FA, Finegold JA, et al. Side effect patterns in a crossover trial of statin, placebo, and no treatment. J Am Coll Cardiol 2021;78:1210-22.
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Educational content only. Not medical advice, diagnosis or treatment. Always consult a qualified healthcare professional before changing your health regimen.