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    Path to Science

    Thinking Dictionary

    Placebo effect

    What it is

    A placebo is a fake treatment. It might be a sugar pill, an injection of salt water, or a pretend operation. It has nothing in it that acts on the problem.

    The placebo effect is the real improvement people feel because of the treatment itself: being cared for, taking something, and expecting to get better. It mainly changes how people feel, such as how much pain or sickness they notice. It does much less, if anything, to what can be measured in the body.¹˒²

    The placebo effect is not the same as all the improvement people show after taking a placebo. Many of them would have got better anyway. Researchers call everything that happens to people given a placebo the placebo response. Only the part actually caused by the placebo is the placebo effect. To measure that part, you need a third group that gets no treatment at all.³

    Why people get better anyway

    This is the key to the whole topic, so it is worth a moment.

    Illnesses often run their course. Symptoms come and go. And people tend to seek help, or join a medical study, when they feel their worst. After an unusually bad day, the next day is usually more ordinary. Scientists call this regression to the mean: unusually high or low measurements tend to be followed by ones closer to average.⁴ It can make natural ups and downs look like real change.

    One analysis found that much of what gets called the placebo effect is really this.⁵ When patients were picked because their lab results were unusually extreme, even their blood tests "improved" by about 10% on later testing, with no treatment at all.⁵

    Why it matters

    You may have heard that placebos are powerful and help about a third of people. That idea comes from a 1955 paper called "The powerful placebo."⁶ But none of the studies in that paper had a group that got no treatment. So the figure mixed the placebo effect with people simply getting better on their own. A later re-check of the same studies found no evidence of a placebo effect in any of them.⁷

    A meta-analysis is a study that combines the results of many earlier studies. The largest one on this question pooled 234 trials (studies that test a treatment on people), covering 60 health problems, that compared a placebo with no treatment. It found no important effects in general. There were modest effects on symptoms people report themselves, especially pain and nausea. Even those were hard to separate from people describing their symptoms in a hopeful or polite way.²

    This matters in everyday life. Feeling better is not always the same as being better. "I took it and got better" doesn't prove the remedy worked. And expecting side effects can bring some of them on.

    In everyday life

    • The remedy that "always works." You reach for a remedy when your cold or back pain is at its worst. A day or two later you feel better, and the remedy gets the credit. But your worst days are usually followed by better ones anyway.⁴ In one study of a gut condition, the group that got no pill at all still improved a lot.⁸
    • Feeling better versus being better. In one study, people with asthma tried four things in random order: a real inhaler, a fake inhaler, fake acupuncture, and nothing. Asked how much better they felt, they rated the fake inhaler almost as highly as the real one (45% versus 50%). But when their breathing was measured, only the real drug helped: about 20% better, against about 7% for the fake inhaler, the fake acupuncture, and doing nothing alike.¹ They felt better, but their airways were not more open. With asthma, that gap can be dangerous.
    • The knee operation. In one trial, 180 people with worn-out knees had either a real keyhole operation or only small cuts in the skin. They didn't know which one they got. Over two years, the real operations never did better than the fake one for pain or for using the knee.⁹ Many patients had felt relief after the real surgery. But it wasn't coming from what the surgeon did inside the knee.
    • Pills you know are fake. Some studies have given people placebo pills openly, saying they contain nothing active. In one small study, 80 people with irritable bowel syndrome (a common gut condition) took such pills for three weeks. They reported more improvement than people given no pills.¹⁰ A larger study of 262 adults found something similar.⁸ This is interesting, but still tentative. The studies were small. People knew which group they were in. The results were based on how people said they felt. And the pills came with an encouraging explanation, which may have done some of the work.¹¹ One review calls this research "in its infancy."¹²

    The flip side: the nocebo effect

    Expectations can work against you too. This is the nocebo effect: expecting harm can bring on real, unpleasant symptoms. Even the way doctors explain possible side effects can play a part.¹³

    In the SAMSON trial, 60 people had stopped taking statins (cholesterol pills) because of side effects. For a year, each took monthly bottles in random order: some with statins, some with dummy tablets, and some empty. Their symptoms were about as bad on the dummy tablets as on the real ones. About 90% of the symptoms that came with taking statin tablets also came with taking dummy tablets. Six months later, half were back on their statins.¹⁴˒¹⁵

    The symptoms were real. The point is that the pill's chemistry wasn't causing most of them. If you think a medicine gives you side effects, don't ignore it, and don't just stop taking it. Talk it over with your doctor.

    The common trap

    The trap is "I took it, I got better, so it worked." The improvement might come from the treatment, from the placebo effect, from the illness running its course, or from a bad day simply being followed by a better one.

    The opposite trap is calling placebo effects "all in your head." For pain, real processes in the body are involved. After dental surgery, a drug that blocks the body's own painkillers made pain worse, but only in people who had been helped by a placebo.¹⁶ Brain scans have shown less activity in pain areas of the brain during placebo pain relief.¹⁷ But real is not the same as curing the illness. There is no good evidence that placebos change the underlying disease.²˒¹

    Some ways out:

    • Ask "compared with what?" Would I have got better anyway? To answer that, a study needs a placebo group, and ideally a no-treatment group too.³
    • Keep feeling and measuring apart. Feeling better matters. But for problems like asthma, check whether something measurable changed too.¹
    • Look for blinding. In a blinded study, people don't know whether they got the real treatment or the fake one. That stops hopes and expectations from colouring the results.⁹
    • Never swap a proven treatment for a placebo. And don't stop a medicine without talking to your doctor.

    Try it: the dice "cure"

    Roll two dice and call the total your "pain score" (from 2 to 12). Keep rolling. Each time you roll 10 or more, call it a bad day. Give yourself a "treatment," like eating a sugar cube or touching a lucky coin. Then roll again and write down the new score. Stop when you've had about ten bad days.

    Now compare. Your bad days scored around 10 or 11. The scores after "treatment" will be close to 7 on average. The "treatment" seems to cut pain by about a third. But nothing caused that. You only treated on extreme days, and extreme days are usually followed by ordinary ones. That is regression to the mean. It is why a study needs a group that gets no treatment, or a placebo, before anyone can say a treatment works.⁴

    A note of caution: keep this to dice and everyday ups and downs. Don't test placebos on real medical symptoms, and don't stop or change any medicine to see what happens.

    Related concepts

    Regression to the mean · Nocebo effect · Blinding · Randomized controlled trial · Correlation vs causation · Confirmation bias · Senses vs instruments · Probabilistic reasoning · Signal vs noise · Indicators of causation

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