Understanding the placebo effect

Understanding the placebo effect is difficult. There are, it seems, more definitions on offer than research groups investigating it — and all are unsatisfactory in one way or another. Difficulties increase when trying to answer some of the many questions that placebos pose. Do we need placebos to generate a placebo effect? What elements constitute a placebo response? Are placebo effects always beneficial? Are some situations more placebo-prone than others? What ethical implication does the use of a placebo have in research or clinical practice?