Placebo and nocebo effects: how expectations change symptoms
A placebo effect is an improvement that comes from expectation and the experience of being treated rather than from an active drug. A nocebo effect is the reverse: symptoms or side effects caused by expecting harm. Placebos can ease symptoms the brain controls, such as pain and nausea, but they do not shrink tumours or lower cholesterol. Nocebo effects are powerful: in one trial, about 90% of the side effects people blamed on statins also appeared with dummy tablets.
Health writers · Aslam Clinic
A effect is a real improvement in symptoms that comes from expectation and the ritual of treatment — the consultation, the tablet, the injection — rather than from any active ingredient. A is the opposite: new or worse symptoms caused by expecting harm, often after reading a list of side effects. Both are real changes in how the brain processes symptoms. Neither can cure a disease.
Understanding them helps you make better decisions about your own treatment — including whether you really need that injection or drip, and whether a side effect is truly coming from your medicine.
What a placebo is, and what it is not
A placebo is a treatment with no active ingredient for the condition: a sugar pill, a saline injection, a sham procedure. In research, placebos let scientists see whether a medicine works better than the experience of being treated.
Not everything that happens after a placebo is a placebo effect. Many symptoms improve on their own, and people often seek help when symptoms are at their worst, so they would have eased anyway. The true placebo effect is the extra improvement that comes from expectation and care.
What the evidence shows — and what it does not
A Cochrane review compared placebo with no treatment at all in more than 200 trials covering 60 conditions. It found that placebos do not have large effects in general. There were small effects on outcomes patients report themselves, most consistently for pain and nausea, and no clear effect in conditions such as , obesity, depression and dementia, though the evidence was imprecise.
As Harvard Health puts it, placebos may make you feel better, but they will not cure you. That is why a remedy that 'made me feel so much better' can still leave blood sugar dangerously high.
How expectation changes what you feel
Symptoms such as pain, nausea and fatigue are not simple read-outs from the body; the brain weighs incoming signals against what it expects. Several processes are involved:
- Expectation — believing relief is coming can activate the brain's own pain-dampening systems. Brain-scanning studies, including in people with knee arthritis, have shown changes in brain activity in those who feel relief after a placebo.
- Learning — if tablets from a trusted doctor have helped before, the body comes to associate the ritual with relief.
- Attention — worry makes you notice ordinary sensations you would otherwise ignore. Starting a new medicine and scanning your body for problems is a recipe for finding some, and then blaming the tablet.
- Anxiety — fear of harm triggers the stress response, which itself produces headaches, a racing heart, stomach upset and dizziness.
These are the same mechanisms behind many . They are real changes in how the nervous system processes signals, which is why the symptoms are real even when the tablet is not.
Injections, drips and expectations in Pakistan
Many Pakistanis believe an injection or a drip works faster and more strongly than tablets, and many clinics are happy to provide them. A 2025 commentary in the Pakistan Journal of Medical Sciences, by authors from WHO and a Karachi research foundation, notes that patients in Pakistan like to receive injections, that providers prefer to prescribe them for quick relief, and that an injection adds income for a private practitioner. Estimates suggest the average person in Pakistan receives between 8 and 13.8 injections a year.
Part of the 'strength' people feel is expectation: the needle, the ritual, the sense that something serious is being done. But the costs are real:
- Infection — the same commentary reports that, of new hepatitis C infections attributed to unsafe injections across 60 countries in WHO's 2024 estimates, Pakistan accounted for 44%. HIV outbreaks among children in rural Sindh in 2019 and in Taunsa, Punjab, in 2025 were linked to unsafe injection practices.
- Blood sugar — glucose ('dextrose') drips and steroid injections given for weakness or aches can send sugar soaring in people with diabetes.
- Delay — a drip that makes you feel better can hide a problem that needed diagnosing.
The nocebo effect and side effects
The nocebo effect is best shown by a UK trial called SAMSON, published in 2020–21. It recruited 60 people who had stopped taking statins (cholesterol-lowering tablets) because of side effects. Each received 12 monthly bottles: four containing a statin, four identical dummy tablets, and four empty — in random order, without knowing which was which. They scored their symptoms daily on an app.
| Month type | Average symptom score (0–100) |
|---|---|
| No tablets | 8.0 |
| Dummy (placebo) tablets | 15.4 |
| Statin tablets | 16.3 |
About 90% of the symptoms caused by taking a statin also appeared when taking dummy tablets. Symptoms started and stopped in the same way for both. Six months after the trial, half of the participants had gone back to taking statins.
This does not mean all side effects are imaginary. A 2022 analysis of 19 large double-blind trials involving over 120,000 people found that statins do cause a small excess of mostly mild muscle pain, mainly in the first year. But more than 90% of muscle symptoms reported by people taking statins were not caused by the statin, and the small risk is far outweighed by the protection against heart attack and stroke — particularly important in diabetes.
Open-label placebos
Researchers have also tested 'open-label' placebos, where people are told honestly that they are taking a dummy pill. An updated 2025 review of 60 randomised trials found a small positive effect, mainly on symptoms and wellbeing that people report themselves. On objective measures the effect was close to zero. The research is interesting, but it is not a treatment to buy, and no one should sell 'honest placebos' as a cure.
The ethics
Giving someone a placebo while pretending it is a real drug is deception, and it undermines trust and informed consent. Giving unneeded vitamin injections or drips 'to satisfy the patient' adds cost and infection risk without treating anything. The honest way to use what placebo research teaches is different:
- A warm, unhurried consultation and a clear explanation improve how people feel and how well they follow treatment.
- Explaining how a medicine works and what to expect helps it feel purposeful.
- Describing side effects honestly and in proportion — 'most people have no problems; a few get mild stomach upset that settles' — can reduce nocebo symptoms without hiding anything.
What this means for you
- Judge your diabetes and blood pressure treatment by your readings, not only by how you feel.
- Before accepting an injection or drip, ask whether tablets would do.
- If you get a side effect, note when it started and tell your doctor before stopping the medicine.
- Read medicine leaflets knowing that most listed side effects are rare, and that many people report the same symptoms on dummy tablets.
- Choose doctors who explain — the explanation is part of the treatment.
Common questions
Still not sure what to do?
Reading about a symptom only goes so far. A doctor who can ask you questions and examine you will get further in ten minutes than any article can.
