Placebo response without placebos

Often, I hear that the placebo response is an artifact, merely a control for the "real" treatment. Today, I'd like to blog about a paper that suggests that every treatment is partially placebo. The paper is Benedetti et al 2003, and is probably one of the most interesting papers I have read.

Essentially, the study looked at whether or not the awareness of treatment had any impact on the response to real drugs. To do this, they used (mostly) post-operative patients and looked at pain & anxiety.


Each treatment was given in two conditions: open and hidden. In the open condition, patients were given a drug by a doctor who told them what they were getting. In the hidden condition, the drug was given without the knowledge of the patients.

The study also looked at open and hidden interruptions in treatment, and the results were essentially the same (i.e. pain/anxiety levels were higher after the open interruptions). 

The results were clear for pain and anxiety. Open infusions were much more effective than hidden ones, with pain decreasing much more in the open condition than in the hidden one.  The drug given for anxiety was diazepam (Valium) and this drug was COMPLETELY ineffective in reducing anxiety in the hidden condition. One could take these results to mean that Valium is a placebo, and only works because people believe it will. Is it the cultural lore thats developed around Valium be the only reason its effective? Shocking stuff, and food for thought the next time someone argues that placebos are "just" controls or have "no clinical significance".

Now, its worth being aware of a few caveats to this study. Firstly, the open condition was actually measuring the difference between the presence of a doctor and the awareness of a treatment. This could be gotten around by using a prerecorded voice telling participants that they were about to get medication.  Unfortunately, no one appears to have done this study yet, but its an interesting question nonetheless.


Benedetti, F., Maggi, G., Lopiano, L., Lanotte, M., Rainero, I., Vighetti, S., & Pollo, A. (2003). Open versus hidden medical treatments: The patient's knowledge about a therapy affects the therapy outcome. Prevention & Treatment, 6 (1) DOI: 10.1037/1522-3736.6.0001a