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The placebo effect: first world congress in Leiden

Medicines can work even if they have no active ingredient. The first international scientific conference on placebos will take place in Leiden from 2 to 4 April. Placebo researcher Andrea Evers, who is also chairing the conference, answers some pressing questions.

The concept of the placebo effect has been around for a long time but it's only in recent decades that so much attention has been paid to it in the scientific world. What has changed? It seems to indicate a paradigm shift in medicine.

‘The past ten years have seen an increase in the attention being paid to research on placebos. On the one hand it has become clearer that placebo effects play a role in more or less all illnesses and all types of treatment. On the other hand, there is growing evidence for the neurobiological effects of the placebo effect. For example, that placebo effects are linked to particular brain activity, such as an increase in dopamine, a substance that promotes wellbeing and is linked to the reward system. An important breakthrough in the research came about with experiments that demonstrated that the placebo effect could be strengthened or reduced if particular physiological substances, such as medicines that increase or reduce pain, play a role. These experiments showed a direct relationship between a placebo and neurobiological changes.' 

'This has contributed to the increasing stream of research on the way in which placebo effects could influence all kinds of conditions and disease processes. The insights gained from this research could in time lead to new treatments. The increasing attention being paid to active mechanisms in medicine that are not the consequence of the presceibed treatment itself, but of factors surrounding it, including doctor-patient communication, can indeed be seen as a paradigm shift in medicine.'

Prof.dr. Andrea Evers

What role is Leiden University playing in the research?

‘Our group - Health, Medical and Neuropsychology - has been doing research on placebo effects for some time. I was awarded a Vidi subsidy from NWO in 2009 for this research, and then an ERC Consolidator Grant in 2013, and this year an NWO Vici. Other countries where research is being done include Germany, the US and  Australia. Our research focuses on placebo and nocebo effects (a medicine can, for example, cause a lot of side-effects if the patient is overly concerned about the treatment) in such symptoms as pain and itching, and on the other hand on the effects on the immune and hormone systems. An important point is how we can use these effects to optimise care and develop innovative treatments.'  

How did this first world congress come about?

An expert meeting was held in 2014, after which the Society for Interdisciplinary Placebo Studies (SIPS) was set up. The Society then decided that it wanted to organise a conference, and we're very happy that we are the ones doing that.'  

What do medical specialists think about the attention that's being paid to the placebo effect? Haven't they been brought up on the idea that medicines have to contain active ingredients?  

‘Medical specialists generally have an open mind here. They recognise from their clinical practice that the way they approach patients and the way they communicate about treatment, such as stressing the risks and side-effects, can have a major influence on treatment outcomes.  It's just that at the present time no systematic attention is being paid to the guidelines. This is something we're trying to change with our research.' 

Is it already clear when a placebo effect doesn't occur? Is placebo chemotherapy, for example, conceivable? In a TV programme in which you appeared, it was made clear that a placebo operation in any event isn't possible. 

‘Placebo effects work in principle for all kinds of conditions, not only for medicines but also for operations and physiotherapy. It has to do with the fact that the placebo effect is an expectation with regard to a treatment; that expectation can have the effect of strengthening the treatment or weakening it. The most important mechanisms involved are conscious and unconscious learning processes. These can be, for example, the verbal suggestions made by the doctor (a conscious learning process) and conditioning (which we know about from the outcomes of experiments on the Pavlov effect). In these experiments a dog would salivate when he heard a bell, simply because previously hearing the bell meant he would be given food (unconscious learning process). Unconscious conditioning processes work best if the previous method used had strong effects - both positive and negative.’

'At the conference we are organising a workshop with international experts to bring together recommendations for clinical practice, such as making use of the placebo effect in doctor-patient communication. Both doctors and patients can benefit from optimum information on this. Doctors can, for example, practise informing highly anxious patients about side-effects and so reduce the nocebo effects.' 

Does a placebo have a lasting effect?

‘A placebo effect can disappear after some time and lose its effectiveness. The expectation then has to be renewed if it is to be effective again.' 

There is an ethical aspect to the use of placebos. For example, if a patient does not know he is taking part in a clinical trial and may be receiving a placebo. What are your thoughts on that? 

‘That's out of the question. As placebo and nocebo effects also work when the patient and doctor are aware of them, it is even more important for clinical practice that everyone involved is properly informed about the effects. That way they have the optimum effect. Then, the question of an ethical dilemma doesn't apply. It is important to realise that the placebo effect only works with long-term expectations. If a doctor claims that a medicine will be very effective, while that is not the case, he will be more likely to cause nocebo effects in the patient when  it turns out that the treatment does not have the promised effect.' 

Is the conference also open for other professionals, including medical experts? 

‘Certainly. We believe it's very important that care providers and others concerned can take part in the conference. There is, for example, an accreditation for GPs and psychologists.' 

More information and how to register


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