An exploration of the relationship between placebo and homeopathy and the implications for clinical trial design.

Placebo appears to be a real neurobiological phenomenon that has evolved through the selection pressure to be able to heal ourselves. The complex language and social structures of humans means that we can attribute meaning to therapeutic encounters with culturally sanctioned authority figures and we can use our attachment to such figures to generate hope for recovery. Different mechanisms may be involved in the neurobiological aspect of placebo including anxiety, learning, conditioning as well as individual genetic variation. Examination of the published work shows that while some trials do seem to indicate a specific mode of action for homeopathic remedies other trials do not and this is an issue that needs to be addressed at the trial design stage. A clinical trial that includes both a placebo group and a non-participating control arm is the most powerful design for separating the non-specific and polymorphic placebo effect from the specific effects of trial medication. The control variables in a trial of homeopathic medication should also include the process of consultation as this may assume a meaning for the individual that can also be associated with a placebo effect.