Australasian Science: Australia's authority on science since 1938

Nocebo: Whatever Doesn’t Kill You Might

By Peter Bowditch

The opposite of a placebo is called a “nocebo”, which is when expectations of a bad effect lead to a bad experience.

The word “placebo” comes from the Latin meaning “I must please”, and is a psychological condition that causes people to respond favourably to medical treatments that actually have no active component. It is based on the expectation that something good is happening, and actually applies to real medicines and treatments as well. Clinical trials are designed to separate real effects from placebo.

The opposite to placebo is called a “nocebo” and is when a bad effect is experienced because of expectations that this will occur.

I’ll start with an anecdote because as any practitioner of pseudo­science will tell you anecdotes are just as good as real data. I have a condition called acrophobia – a fear of heights. This is an evolutionary trait, because people who went too close to the edges of cliffs often didn’t live long enough to leave offspring. In my case it isn’t really a fear of heights but a fear of falling – I have no problem on the balconies of apartments in tall buildings or on walking trails with handrails on mountain cliffs because I have something to firmly hold onto.

On a holiday in Central Australia a few years ago I did the then-obligatory climb up the rock at Uluru. At a particular point on the climb you can be presented with an optical illusion of being suspended in the air. I reached this point, looked down and was paralysed. It took me about an hour to climb the next 100 metres until the illusion disappeared. As I said to someone later, if someone had given me a writing pad and a pen I could have written a useful essay on why the curvature of the rock at that point generated the illusion. It didn’t help that I knew exactly what was happening in my mind and that the rock had been there for many millions of years without becoming airborne. I knew I was experiencing a nocebo effect, but knowing that didn’t help.

A common manifestation of nocebo is it when people claim sensitivities to certain foods. Yes, there are people who really are sensitive to gluten and some who cannot ingest dairy products; there are people with legitimate allergies to the proteins in certain foods. There are those like me who have to be very careful about the amount of carbohydrates in foods. There are also people who claim to have sensitivities but only exhibit symptoms when they know that they have consumed the offending chemicals.

A classic nocebo effect with food is the “Chinese headache” caused by monosodium glutamate. MSG occurs naturally in tomatoes, mushrooms and Parmesan cheese but I have never heard of anybody suffering from a “pizza headache”. Most Chinese restaurants now display signs saying something like “No added MSG” which seems to solve the problem of people suffering bad reactions to the MSG that is inevitably already in the food.

A friend of mine was recently at a dinner where pumpkin soup was served. A nearby vegan was commenting on how delicious it was until he was told that it was made with chicken stock, at which point he changed his opinion to how bad it tasted.

I was once a guest at a Chinese New Year dinner where the set menu was written in Chinese characters, and I had never before seen anything that was placed in front of me. When leaving, I told the host that everything was delicious but if he ever told me what I had been eating I would never go to his restaurant again!

The nocebo effect doesn’t just apply to food. The symptoms of Wind Turbine Syndrome or the effects of electromagnetic radiation from mobile phone towers (and now the towers used for wireless distribution for the National Broadband Network) only seem to happen to people who oppose the offending structures for some aesthetic reason. There seems to be a correlation between “I don’t like the look of that” and “It’s making me sick”.

A few years ago a large country town announced impending fluoridation of the water supply. The inevitable complaints and objections were raised and immediately following the date that it was to be turned on reports started coming in of dead lawns and even of goldfish dying when their tanks were topped up. The council eventually announced that due to a technical problem fluoridation hadn’t actually started on the scheduled date.

And one last anecdote: when I sat down to write this I suffered the nocebo effect familiar to all writers – writer’s block triggered by the word “deadline”.

Peter Bowditch is a former President of Australian Skeptics Inc. (