The placebo effect: what expectation can do, and what it cannot

In clinical trials, some patients receive the real drug and some receive a pill that looks the same but contains no active substance. That is the placebo. Its purpose is to show how much of the improvement comes from the drug, and how much from everything else: time, the doctor's attention, the patient's expectations. Often the placebo group improves more than expected.

What the placebo effect is

The placebo effect is the improvement that comes from the context of treatment, not from the substance. It includes expectations ("this will help me"), past experiences of treatments that worked, and the ritual of care: the visit to the doctor, the explanation, the very act of taking a medicine.

Studies show that the placebo effect is strongest for symptoms that are experienced subjectively and shaped by the brain: pain, nausea, fatigue, anxiety, some bowel symptoms. With pain, for example, expectation can activate the body's own systems that dampen it.

Placebo without deception

For a long time it was thought that a placebo works only when the patient does not know it is a placebo. In 2010 Ted Kaptchuk and his colleagues at Harvard tested this idea with patients with irritable bowel syndrome. Half were given pills they were told plainly were placebos, "like sugar pills", with the explanation that placebos have shown effects in studies. After three weeks these patients reported more improvement in their symptoms than the group that received nothing.

The study was small, and the patients knew which group they were in, which can affect reporting. Later studies of open-label placebos have given promising but still limited results.

A placebo does not act on the disease. It acts on how the brain experiences it.

Where the limits are

The placebo effect does not shrink a tumour, kill bacteria or heal a fracture. In a well-known study of patients with asthma, a placebo inhaler made patients feel better, but lung function improved only with the real drug. That is why a placebo cannot replace treatment, even when it makes us feel better.

What we can take from it

• Expectation matters. When we understand why we are taking a treatment and believe it makes sense, we experience it differently.
• Ritual matters. A calm conversation with the doctor, enough time and clear explanations are part of care, not a luxury.
• But the body needs the right treatment. The mind can ease symptoms. The causes of disease need medicine.