The potential of a placebo/nocebo effect in pharmacogenetics.

Pharmacogenetic testing holds great promise to improve health outcomes and reduce adverse drug responses through enhanced selection of therapeutic agents. Since drug responses can be manipulated by verbal suggestions, it is of particular interest to understand the potential impact of pharmacogenetic test results on drug response. Placebo and nocebo-like effects may be possible due to the suggestive nature of pharmacogenetic information that a drug will or will not likely lead to improved health outcomes. For example, pharmacogenetic testing could provide further reassurance to patients that a given drug will be effective and/or cause minimal side effects. However, pharmacogenetic information could adversely affect drug response through negative expectations that a drug will be less than optimally effective or cause an adverse response, known as a nocebo-like effect. Therefore, a patient's perceived value of testing, their understanding of the test results, and the manner in which they are communicated may influence therapeutic outcome. As such, physicians should consider the potential effect of pharmacogenetic test results on therapeutic outcome when communicating results to patients. Studies are needed to investigate the impact of pharmacogenetic information of therapeutic outcome.