The nocebo effect: a reason for patients' non-adherence to generic substitution?

Substituting generic formulations of the same chemical agent is a common practice in German health care on the basis of so called rebate contracts. The substitution of a medication may affect the patients' adherence or result in adverse events. While adverse events which may be caused by the pharmacological activity of the agent itself can be explained, some non-specific side effects cannot be substantiated referring to pharmacological factors. These adverse reactions are summarized under the term nocebo effect. Since patients experiencing a nocebo effect can subsequently become non-adherent or even discontinue an appropiate therapy, the aim of this article is to study patients' adherence to generic substitution and the extent of the nocebo effect. In MEDLINE and EMBASE, a search was carried out for articles which were published between March 25th, 1989 and March 25th, 2009 by using the following search terms: generic substitution, adherence, non-adherence, non-persistence, rebate contracts, patients' attitude, nocebo, negative placebo effects, placebo adverse reactions, placebo induced side effects and negative placebo responses. In addition a manual search was performed in the reference lists of the articles retrieved. 14 studies met the inclusion and exclusion criteria and were included in this article. The generic substitution was generally accepted by over two thirds of the study populations. But up to 34% of patients being treated for psychological diseases confronted with a change of their medication had additional adverse events. On the basis of the studies analysed, the conclusion can be drawn that the nocebo effect can play a crucial role in the treatment of psychological diseases. Therefore, physicians and pharmacists should be responsible to prevent the nocebo effect through adequately educating the patients.