Do placebos help against itching?
If a pill containing no active ingredients still helps, this positive expectation is called a placebo effect. A negative expectation is called a nocebo effect. Both can be produced by verbal suggestions and conditioning. According to Andrea Evers’ research group, combining these is the most promising approach to itching.
Placebo effects play an important role in many conditions in medical practice. For example, merely having a positive expectation can influence the effect of a treatment. Research into the placebo effect has really taken off in the past few years, and more and more is becoming known about its effect on a large number of physical disorders. The reverse is also true: a negative expectation can also play a role in the outcome of a treatment. This so-called nocebo effect can decrease the effectiveness of a treatment.
Placebo and nocebo effects are based on learning mechanisms. You can thus direct your expectations with verbal suggestions like ‘this pill works for a lot of people’. Conditioning also comes into play, with the pain decreasing at the mere sight of a painkiller. A lot of research has already been done on the effects on how people experience pain, but much less is known about these effects on itching. Andrea Evers’ research group is attempting to get a better picture of the mechanisms at play with physical symptoms like itching. Several years ago Evers received a Vidi grant from the Netherlands Organisation for Scientific Research (NWO) to do just that.
In her research, PhD candidate Danielle Bartels compares the two learning mechanisms – verbal suggestions and conditioning – in relation to itching stimuli. The results shows that the combination of a verbal suggestion and conditioning is particularly effective for nocebo and placebo effects. This is in line with earlier findings about pain. Combining the two learning methods to produce positive and negative expectations seems to also be the most promising method for placebo and nocebo effects with itching.
In Antoinette van Laarhoven’s PhD research, the research group had already shown that with itching it is particularly nocebo effects that can be produced relatively simply by a verbal suggestion. Test subjects who in a laboratory setting are told that a stimulus causes itching in 95% of all test subjects react to all stimuli with more itching than do test subjects who are told that a stimulus only causes itching in 5% of all test subjects. That was the first clear evidence that nocebo effects also play a role in itching.
Follow-up research should show whether these effects can also be modified. This is important for clinical practice with unintended nocebo effects, such as when information about the risks of side effects is given to patients who are overly fearful of side effects from their medication. Evers was recently awarded an ERC Consolidator Grant. With this European grant she will conduct research into conditioning the immune system and the hormone system.
(22 April 2014)