Placebo vs Nocebo: A Powerful Mind Game

You have been visiting your doctor, and she was concerned about your blood pressure. You knew that you had a horrible day and probably was a one-off occasion, and believe if you rest, your blood pressure will normalise. You have read a lot about the side effects of the medications and have been trying to avoid them. The doctor eventually twists your arm and prescribes the medicine for you. You go home and read the pamphlet, which has listed many “likely” side effects. After a few days, you feel like you are experiencing all these side effects, and you stop the medication. Another person who doesn’t worry about side effects will take the same medicine, with absolutely no problems. Here a complex mental game is in play that stops you from taking a critical treatment. 

Before diving further into the topic let’s define some important terms.


A placebo is any medication or treatment taken, which you believe will help you, but has no therapeutic benefits. They are mostly weakened sugars, with no biologic effect.


A nocebo is any medication or treatment taken, which you believe will harm you, but is actually not harmful or painful. This could be a medication, procedure or vaccine.

Placebo Effect:

The placebo effect is when you take the placebo, and you actually feel better. Simply because you believe it will help you, it does.

Nocebo Effect:

The nocebo effect is when you take the nocebo, and you experience side effects. You have convinced yourself that it will cause harm. Simply because you believe it will harm you, it does. Think sick, be sick.

In a recent, well-done study SAMSON Trial, it’s shown that most patients who could not tolerate life-saving statin therapy were experiencing the Nocebo effect. Most of them could re-start statins with no further pain after six months. Statins are critical medications in people at high risk of ischemic heart disease, and depriving patients of these medications can significantly increase the risk.

It was shown in another study, ORBITA Trial, that patients who underwent a sham (fake) coronary angiogram, did have some improvements in their symptoms, despite not having coronary angioplasty. Just because they BELIEVED they had an effective procedure and treatment, they felt better.

In daily practice, we do notice many other examples. A very interesting one is when patients have an echocardiogram or stress echocardiogram. Although these are only diagnostic tests with no therapeutic effects, many individuals feel better as they “believe” something has been done for them and expect the healing effects.

How the mind controls the body and symptoms?

Despite years of investigation, there is no clear answer about how the mind controls the body in this fashion. What is known is that these phenomena are real and extremely powerful. They can make a considerable change in patients lives, for good or bad.

While the Placebo effect can be quite positive and helpful, the Nocebo effect can deprive you of accepting a life-saving treatment. You have convinced yourself that some specific therapy will harm you and should be avoided. This idea stems from deep beliefs you have formed during life and maybe negative past experiences, certainly going back to childhood. Changing a “cemented belief“, right or wrong, is a highly challenging task. If you strongly believe eating pork is not acceptable, for religious, medical or eco-conscious reasons, getting you to try pork would be highly unsuccessful.

If you believe COVID-19 is a hoax and vaccines are manufactured to decimate humans from the face of the earth, you will avoid vaccination. With that mindset, if you choose to get vaccinated, as you have to for whatever reason, you will probably experience more side effects! Your mind is “set” to experience side-effects and is not satisfied without them! You were expecting them.

How Nocebo effect plays a role in patient’s outcomes?

The nocebo effect is a crucial player for better communication in healthcare settings. For example, before prescribing a medication, you might say, “This may cause headache.” With this comment, there is a high likelihood the patient will return with a headache. But what if you say, “Most people feel no pain at all”,? Adding a simple “only” to the phrase, “only one per cent or an absolute minority of people taking this drug might have a headache”, will reduce the patient’s expectation of having a headache and they will have less headache!

Talking about this phenomenon with patients could also help to shed more light on the mind-body connection and how your mindset can influence your physical health.

Accepting a medication or treatment depends on many factors, including patients’ trust in their doctor, past experiences with the same therapy, and how the doctor provides information. Due to ethical obligations and full-disclosure laws, a doctor has to provide the data. But, the way this information is presented can make a huge difference to patient’s outcomes.

Placebo vs Nocebo Dr Moazzeni
Placebo vs Nocebo - SAMSON Trial

In Conclusion:

Our thoughts are so powerful that they constantly push us towards our goals even when we don’t realize what those goals are. Whether they are good or bad for us, as long as they are “goals”. Our brain is wired to win. This dynamic doesn’t just apply to our health. It plays out in our relationship, career, fitness and everything else we do. We are hard-wired to win.

In the case of Nocebo, our goal is to prove we were right, and some treatment or medication isn’t good for us. Our brain plays any trick to win the argument, even at the expense of our health.

On the other hand, if our brain decides that something is good for us, we feel good even though there is no objective proof of that. That’s what Placebo is.

Placebo and nocebo effects are powerful and very common in daily medical practice. Neurobiological mechanisms, how information is given about treatment, patient’s expectations, previous encounters with a drug or procedure can all generate these effects. 

Strategies to promote placebo effects and prevent nocebo effects can improve outcomes and minimize unwanted symptoms in daily clinical practice.

Dr Reza Moazzeni MD, FRACP

Dr Reza Moazzeni MD, FRACP

Dr Moazzeni is a Consultant Cardiologist practising at Westmead and St Leonards in Sydney, NSW. He has a special interest in cardiac imaging, including Echocardiogram, Stress Echocardiogram, CT coronary angiogram, coronary artery calcium score, and preventive medicine.

Heartcare Sydney

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