Placebo and Nocebo — When Belief Becomes Genuine Medicine, or Genuine Poison

In clinical trials, before a new medicine is released, patients are given a dummy pill to see what happens. Some genuinely report their pain improving, though what they swallowed was pressed starch. But everything in this world has its light and its shadow. Where some recover on a dummy pill, others read the list of side effects on a leaflet and begin to feel nauseous and headachy — before taking anything at all.

Do not mistake this for imagination. These are the phenomena known as the placebo effect and the nocebo effect, and both are evidence of how powerfully belief and expectation act on the body, at a level science can measure.

What placebo is, and why it is not merely imagination

The placebo effect is the improvement a patient feels after treatment containing no active substance, simply because they believe and expect it to work.

Brain-imaging research finds that when a patient believes they are receiving pain treatment, activity genuinely falls in regions involved in perceiving pain, such as the insular cortex and thalamus. The body also releases several neurotransmitters associated with natural pain relief — endogenous opioids, dopamine and oxytocin. In plain terms, belief does not merely trick someone into feeling better. It prompts the body to produce chemistry that genuinely eases symptoms.

And nocebo?

The nocebo effect is the reverse. Negative expectation — fear of pain, worry about side effects, a belief that things will worsen — produces genuinely unwanted symptoms: increased pain, nausea, other discomforts, with no medical cause behind them.

A striking review of COVID-19 vaccine trials found that people given the dummy injection in control groups reported a considerable number of side effects, though they received no active substance at all — showing that expecting side effects is enough for the body to produce them.

How the brain builds belief, and why it reaches the body

The mechanism behind both is what researchers call expectation. Expectation is shaped by prior learning, by watching others, and by what we are told — and it acts directly on the body’s own machinery for governing pain.

Research has found that the hippocampus, the region concerned with memory and learning, plays an important part in extending the nocebo effect to new situations resembling something that hurt before, even without the identical trigger. Which means the brain can learn to fear, or learn to expect improvement, and carry that influence into new situations more widely than one might think.

What this has to do with hypnotherapy

The principle behind placebo and nocebo resembles what happens in hypnotherapy. Both show that belief, expectation and suggestion genuinely change how the nervous system and the body work — not merely how something feels.

Hypnotherapy works with that same principle, deliberately and with direction: using deep relaxation so that constructive suggestion can reach the nervous system more effectively. Where the nocebo effect shows the harm of negative belief left to run unnoticed, hypnotherapy can help resolve the negative beliefs and expectations settled in the subconscious.

Put another way: placebo and nocebo are clear demonstrations that expectation and belief genuinely change the nervous system and bodily perception — and hypnotherapy is one instrument that puts this to purposeful use.

One thing to be clear about: the placebo effect does not mean pain is not real, and it does not mean positive thinking alone can resolve serious illness without medical treatment. Most of the research shows placebo effects chiefly in the perception of pain and in symptoms involving the nervous system. It does not mean belief can replace treatment for a physical illness with an established cause.

What is worth understanding is that belief and expectation are genuine factors in the experience of illness, and that understanding the mechanism lets us use that power more usefully — rather than leaving fear and worry to build suffering unnoticed.

There is also current research on open-label placebo, where patients are told plainly that what they are taking is a placebo, and in some conditions interesting effects are still found — a reminder that the power of expectation is more complex than it appears.

We regard placebo and nocebo as the clearest demonstration of something we have always held: that mind and body are not separate.

The beliefs we build in our heads, knowingly or not, genuinely affect the body. And that is why working with patterns of belief and expectation in the subconscious means more than many people suppose.

To understand how imagery works in the brain, see “The Brain Does Not Know the Difference Between Doing and Imagining”. And for why attention affects pain, “The More You Attend to It, the More It Hurts” makes it clearer.